You know, I hate to say it, but I think this thread is starting to take a turn I wasn't expecting. When I created these feats I honestly only wanted to create something that would take advantage of all the unused durations so many spells had after they served their immediate purpose.
For example, after you've checked out a room with Detect Magic you usually still have some duration left on the spell. Wouldn't it be nice to save it for later?
Or you just finished a battle and your Shield spell still has a few rounds left to it...too bad you have see them go to waste. If only you can save those few rounds of potential until the next battle...
Basically, it was simply a way to turn one casting of a spell into two or three castings of lesser durations. I'm sure we can all think of tons of utility, non-combat spells that would benefit from this type of thing.
It's unfortunate that you guys are finding all these killer, unbalancing, combat oriented uses for it. Well, maybe it's not unfortunate, I mean better this stuff comes up now, during the development phase right? But, it does mean the feats need a lot more tweaking before they become what I had originally invisioned.
I think Billking has the right idea then. In order to keep this from becoming a powerful "sneak attack" type of feat, it may be best to keep the reactivation time exactly the same as the spell's original casting time. You know, it even makes sense somehow. That way, the feat truly becomes what I just described: two or three shorter-duration castings for the price of one.
Maybe the feats should be changed drastically and renamed to "Split Spell"?? That way, the duration is not really being suspended at all. Instead, the caster takes a spell and splits it into two or three equal duration pieces, all needing to be cast just like the original. How about that?
Heck, it can even be recorded on the character sheet as two entries: "Split Shield 1" and "Split Shield 2", both pieces occupying a single higher level spell slot. The fact that they are listed as being Split, we know that there durations should be half normal.
Of course with the Split versions we then lose the advantage that the Suspend versions had of being able to split the duration anywhere we wanted, not just in half.
So, what say, Suspend Spell or Split Spell??