One thing that I will note... elite and solo monsters stay the same CR, but will provide a larger difficulty to the party. So they give the same reward for a more challenging encounter. I'm guessing this is plot protection more than anything else? I might houserule this, if I can't figure out(and subsequently agree with) the design philosophy behind it.
Two comments:
ELITES
As you can probably guess from Chapter 1, adding 1 AP and doubling the hit points of the critter isn't going to change its CR noticeably. Doubling the hit points is akin to going from a d6 to a d12. The AP is negligible. When I DM, it's basically there to prevent rocket tag.
SOLOS
This one is actually a little more complicated, because the gains are so much greater. A Solo gets 1 AP
per PC and you multiply its hit points by
the number of PCs.
What's not explicitly called out in my explanation (which you're making me regret...) is that a single creature-- remember, a Solo MUST be alone-- is already at a huge disadvantage against a larger number of PCs.
This is extremely difficult to explain in short form, which is why I did not really get into it, but a Solo creature runs smack up against Lanchester's Square Law, and therefore
it is not as powerful as its CR indicates when it is alone.
You have probably experienced this already in 3e. BBEGs tend to die a horrible death as they are overwhelmed by a party of PCs taking 4 actions to its 1 action.
The benefits the Solo get don't increase its value over its CR, such that the award of extra XP is warranted. Instead, the benefits the Solo get bring it up to its CR, so that it is worth the XP you were already intending to award.
Clear?
EDIT: I think perhaps Chapter 1 got me a little squeamish about providing really long, pedantic explanatory notes on stuff, but if folks want more of it, I can certainly roll it in.
I'm giving myself a bit of time before the print version for just that reason.