I really don't see a reason to give those funds back to masternodes or miners "who were there" because the fact that taking 15% out in the first place, reduced the number of masternodes and miners. When you put it back in each block reward, you will increase the masternodes and the miners, with each one getting the same rewards they previously got. The pressure of income (ROI) is what prompts people to create Masternodes or mine, and they create them quickly when they see it's an acceptable return. We have been seeing the same number of coins as a reward for quite a while despite the fact that the reward has been going up 2.5% each month.
Anyway, i really think that's the best way to go:
set 15% now, as per Evan's proposal.
Set a top limit to any excess funds to be reserved in savings, and return the rest through block rewards.
re-evaluate the 15% every * years to see if it merits being reduced. reducing it would help masternode owners and miners plan for the future (mine more/set up more masternodes)
Hell, and we haven't even scratched the surface here of how to manage / pay projects or even the voting requirements (percent of participation) and probably a dozen other issues, LOL. Isn't this fun?
Camosoul quote: "You been out there with the hippies too long...

" LOL, You know I absolutely adore you, right? But I think you're not seeing what I'm trying to say. I totally agree, spending must be curtailed if not in everyone's best interest, and no pork barrel projects. I totally agree!