The performance wouldn't be that much different than your 325i. I've never driven an FR-S but I assume the other guy is right. I have 85k miles in my '06 325i, and I've still got no problems at all. The water pump/thermostat/starter problems you list aren't that much to fix if you can find a good indy or can DIY. Besides that, it's not like it's just gonna blow up any minute because of what you consider higher mileage. In fact, my previous 1997 528i had 204k miles on it when it came time to sell it, and even that is still a reliable car with simple maintenance.
Also, as a college student, I appreciate the good use of space the E90 has, plus the whole having 4 doors thing. It comes in handy.
18" Staggered Style 189 - BMS 15mm - CF Grilles - LCI Headlights - BMW Performance CF Intake - 12" Blaupunkt Subwoofer