Well, since the work you are doing is either maps or relatively small projects for the church it all comes down to what you want to deliver. If you are doing a church newsletter and want to create artwork for it either will work, though I find Photoshop more flexible as illustrator's primary strength isn't needed for the job.

However, I only use Photoshop currently because I have it left over from my time as a Graphic Designer. If I had to pay for it, I probably wouldn't. I find that the upgrades between CS, CS2 and CS3 are pretty incremental and don't affect my day to work. Since I am opposed to a cracked version, I'll probably switch to GiMP when I am forced to leave Photoshop CS (version 7).

I was a late adopter to illustrator as I was originally trained in Freehand. Since I am not creating art that needs to scale freely any longer I don't find myself opening illustrator often. Windows says I last used the program on October 21, 2007.

This is all based on how you will be using the programs. If you are only using to crank out fast maps for your tabletop gaming then you'll be fine with whatever you currently use. At least that's my situation. But with the work for your church you may consider keeping the old version of photoshop and using the money for a new copy of illustrator.

Another thing to consider is that if you get into video presentations, final cut pro can use photoshop and illustrator files natively. So if that's an idea for the future, be prepared for it if you decide to ditch adobe in favor of GiMP and Inkscape.