"Your opinion", yes, an opinion - my point exactly thanks.
1) Like you said this is just opinion, having an extra 2 matches after the beginning of the season seems a minor thing to me. You win the PL/FA Cup & you have the community shield, which is way before the qualifying matches for CL (in fact before the season starts) and usually a much "tougher" match on paper. I don't see either event as preseason ruining - I trust the owners will have planned for these scenarios way in advance & made the appropriate plans.
2) In 2014/15 this was £2.9m from what I can see? I'm not sure how much higher this will be (I'd guess closer to £4-5M - where have you gotten £10m from?), but even £10m* still seems fairly minor to me when you see how much clubs earn. Again that is an opinion, you may think that us earning an extra £4-5m* is make or break for the season, but I'd be surprised if it had a huge impact (or that it would be something that motivates players to come 3rd not 4th).
I actually said your statement about results in my comment, if the results go a certain way (i.e. West Ham win some of their games in hand) then by the time we play Stoke/Sot'on they could be playing for nothing.
As for huge financial boost, unless I've missed a big source of income (feel free to point it out, my knowledge on this is fairly crap), like I said a few extra million doesn't seem like it'll make or break the bank for City/Arsenal - especially when you look at other sources of income, some teams earn £70M+ a year on kit sponsors alone.