this
http://www.pprune.org/private-flying...ing-costs.html thread probably contains what you're looking for.
Like aluminum from all aircraft vintages, as long as it has not suffered obvious damage from being overstressed, and is otherwise airworthy, it can be maintianed airworthy indefinately, in non pressurized GA aircraft.
MOGAS is a perfectly fine fuel for the C-150, I have more than 2300 hours running mine on it - never a problem.
I would steer away from IFR in a 150. Aircraft of this type just do not belong in those actual conditions. Yes, you can train and practice, but for safe IFR you want either a high perfomance single, certified for known icing, or an equivilent twin. IO-540 is going to give you a slightly different point of view, but even he will agree that a 150 belongs VFR...
Have a look for an older book by TAB publisher, "The Cessna 150 and 152" by Clarke.