I'd say it is worth it if you play pretty often, but as you said you aren't a hardcore gamer, I'd say no, it isn't worth it. I changed from FF EX to G25 myself and certainly it is a great thing to have, It does it job well, but I was playing quite a lot more back then. Considering it's price, I wouldn't buy it right now certainly, as I will just waste a lot of money on a great piece of hardware, which I will seldomly use on weekends.
In your situation I'd rather buy something like DF GT wheel, which is cheaper, and does most of the features of G25 pretty well. It doesn't have a shifter (which is quite crap feel-wise on a G25) or a clutch pedal (which you can easily have from your FF EX pedals, not the most estetic soloution, but worked for me well).
So, in conclusion: If you have a lot of spare money, why not? If your budget isn't big, buy a lower class wheel.
Just my 2c,
Art.