If you're (not you, obviously, pem) as fond of world|mechanics consistency as I am, +5 levels to make a minion doesn't quite cut it (the result is lower-exp value than the original monsters, which feels off to me, like it's "not really the same bandit" - I guess this is where a "sub-standard/dopple-minion" secondary role might've been nice). A level-5 creature is going to be a tad comical, missing 75% or so of the time and being hard to miss, while it's hps still cause it to stick around for a bit. But, it can give the players the sense that they've advanced since last fighting such things, and a corresponding sense that the world isn't just advancing in lockstep with them - not giving exp & simply hand-waving once the mismatch has been established is a fair way of handling such an encounter, as is turning it into something else, entirely (like a skill challenge to corner the bandits, with the combat to capture/exterminate them not played through), or complicating it with some other objective that makes it more difficult.
I'm not sure what your point is here. Consistency with what? There's no world run by rules in which all bandits must be 8th level standard creatures which making them level 13 minions is inconsistent with. The world is not numbers. If he makes some 13th level minions and calls them 'bandits' they are simply a certain set of bandits who are fairly minor plot devices! He could thus make the encounter 16 minion bandits and a standard leader (or make it 20 minion bandits, a standard lieutenant, and an elite bandit leader to make it a bit tougher encounter). Now its a fairly numerically substantial band which seems logical, but most of them will melt before the PCs, after perhaps mounting a brief threat, leaving their leader(s) to decide when to call uncle.
Anyway, I agree with [MENTION=42582]pemerton[/MENTION] on the levels of things. I'd also alter the Spinagons to something of 13th level. Actually, as the encounter is written, its a pretty easy encounter, one 13th level standard and 4 8th level standards. Simply upleveling the Spinagons would work, but you could also do something more interesting. Perhaps Hathag has 4 daughters! Another option would be to make Hathag into a Solo, which is a pretty standard sort of concept here. The summoned creatures can then be minions, and you could rework the ability so that one or two are summoned every round, or at certain intervals.
Another option here would be to make the whole thing more interesting. How about Hathag has gotten worried about the PCs, noting how they're potentially tough enough to take her out, and she's in the midst of opening a portal to Hell! Best get that closed before too much stuff comes out... (I know, this is a well-worn cliche situation, but as it stands the whole encounter is quite static, it will be a dud, trust me).
And this is the other place where the whole adventure BEGS to have some improvements, is in terms of being dynamic! The party meets some bandits out in what is described as flatland basically and has a fight. They meet up with a Shipwreck Golem, which seems like an interesting creature potentially, but there's not REALLY terrain, everything is difficult terrain. How about if the golem is ON the shipwreck? Its made of PARTS of the ship, and maybe it can even tear off pieces and use them to 'fix' itself as a power! It can smash holes in the deck, knock down masts, smash rails, etc. Now you've got something interesting! If the PCs get off the ship and go into the icky swamp, well they can do that too. Maybe the thing can actually raise the water and turn the only partly swamp area into MORE swamp and deeper water too! Another option might be to have some sort of a condition under which the golem can be pacified. Maybe it just wants something. Maybe the PCs acquired the ship's bell (the bandits had it?) and ringing a change in the watch will cause it to stand down!
Likewise any encounters in the temple itself, such as with Rethaq should involve changes in circumstance, or SCs built in to do something (break the spell of Hathaq?), etc.
The spell itself feels a bit like a gotcha! Is it intended as a 'ticking clock'? If so then the PLAYERS need to know its ticking! Maybe one way to handle it would be as a grand SC where they get some clue that things are not quite right, but they have to gather enough evidence to convince themselves and allow them to break the illusion. I'd also give them a chance to snap other people out of it! Maybe give them a 'canary', like someone they find wandering who left the city and lost Hathaq's influence. This person comes back with them and starts to exhibit strange behavior (IE the influence is starting to take hold again). As the characters note different things they can make perception checks, history checks, arcana checks (this 'spell' does leave magical signs of itself, maybe including signs that it is maintained, like runes or something drawn in various places that the citizens cannot see). If the PCs can figure things out in time (IE win the SC, then they can avoid the influence). It could also be handled as a disease track, but I think the SC mechanism is best.
The final issue with Prosperity's Influence is, what if the PCs simply fall victim to it? They could well just wander the city for a week and all end up so disadvantaged that they cannot win a fight, even if they somehow manage to start one! This isn't even unlikely! I mean, the players know nothing of any problem with the city. Nothing is telegraphed to them in any way, and the spell is specifically described as not having any telltales the would know about (assuming they aren't actually attacked). If I were one of the players, I'd assume this city was simply a location in which to abide for a time, take on some urban adventures, and generally kick back. Yes, its a bit mysterious as to why nobody knows about it, and where the lake went, but you don't even HAVE an answer for any of that within the material ANYWAY! My point being, it would be a pretty paranoid set of players who would immediately assume the worst and imagine they were on some sort of clock! So I'm skeptical this aspect of the adventure, as it is developed now, will even come off as you want (I assume that being that the players cotton to the whole thing and most of the PCs reach the final encounter without being totally disabled).
