Do you need to run Windows for those racing apps? If you do a dual boot system you need to consider how much drive space you'll need. MB Air only has SSD in 256MB (or 512MB for +$300).
SSD is great for really fast boot and file access but, depends on how much storage space you need.
You can do a side by side compare of macs on apple web store..
http://store.apple.com/us/compare/mac?page=mac
13" MBair 1.7g i7, 8GB ram, 256ssd is $1550.
13" MBpro 2.9g i7, 8GB ram, 750hdd is $1500.
13" MBpro 2.9g i7, 8GB ram, 256ssd is $1800.
1.7ghz i7 might seem a little slow if you do any heavy graphics/photoshop work so, I hope you do mean 'light' graphics/video work.
MBair actually has a better GPU than MBpro
Intel HD Graphics 5000 vs 4000 comparison..
http://www.anandtech.com/show/7072/intel-hd-5000-vs-hd-4000-vs-hd-4400
And, MBair has 802.11ac - newer than 802.11n on MBpro.
MBpro has DVD drive and extra ports for firewire & ethernet. But, you could always get an external DVD and dongles for MBair if you need those.
4+ year life span is possible. But, the computer might have trouble keeping up with newest OS and software 4 years from now.
Usually, I suggest selling your old mac at around 3yrs old and get a new one. 3 yr old Mac in decent condition should still have a good resale value that will make a good percentage for buying a new Mac.
You might also look for a Mac on Apples Refurbished page. Refurbs are all tested and certified with same 1yr warranty. They're clean too, not worn out or used looking. They're not configurable so, it's hit and miss to find the model you want, just check weekly. Look at the "Originally released.." date to see which year you're getting. But, you might not see new models like June 2013 MBair on Refurbs until a few months later.
http://store.apple.com/us/browse/home/specialdeals/mac/macbook_air
You might also consider getting AppleCare extended warranty - extends standard 1yr to 3yr warranty - free repair of hardware failures (not including damage you cause of course). But, you don't have to buy it when you get your Mac. You can wait and buy it later, anytime before your 1yr expires. Keep your eyes open and find it on sale somewhere.
Also, check on MacRumors buyer guide to see release info..
https://buyersguide.macrumors.com/