I'll give you another perspective that can help you. I use an iMac from mid 2011. For my daily and personal computer use I always prefer a Mac, it works better for my life, but I wish I had a gaming PC dedicated just for flight sim. I put my money into my flying career rather than sim flying so for now I do not have a gaming PC. I do however use FSX on my Mac in Windows 7 64bit. Everyone knows that a Mac's hardware is not geared for gaming, but here's my specs to give you a perspective on that you can do. 2.7 GHz i5 processor, 8 GB of RAM and only 512 MB of video memory from an AMD 6770M. I run the PMDG 737 and 777 on it as well as many great airports and sceneries from UK2000, Orbx, Flightbeam, FSDT, Taxi2Gate, FlyTampa, and so on. I run ActiveSkyNext, and I have run AI traffic, but I found that tends to push it a little far and it crashes after a while, so if I want some traffic I stick with VATSIM flying. My settings are obviously not super high, but scenery, and aircraft look good, and my frames are often in the mid to upper 20's which is totally fine.
There are some airports that just do not work well with this system. LatinVFR's Miami V2 works, but the frames are in the mid teens to low 20's, but all other LatinVFR works. Other big complex airports work, like Flightbeam SFO, UK2000 Heathrow, Taxi2Gate Istanbul, and so on work very well. I don't know the rhyme or reason why one complex airport works very well, and another is just terrible. Lighting at a 3rd party airport can be a big problem. For example Geneva, I can fly in there during day VFR, but IFR or night when lights are on, then the frames are terrible. Belgrade V2 works great when there are no approach lights. All other lights at this airport are fine, just approach lights cause problems for me. At UK2000 Heathrow, I can do night flights no problem, and it looks very nice.
Ultimately what I'm getting at is yes with older and under performing hardware you can still have a good experience, but if you are able to upgrade or over clock some stuff, I'd do it.