Gels take 20 mins or so to kick in anyway - so if you're feeling the benefit of them its probably just psychological.
That's why I take them in plenty of time - around 8 miles on training runs, and just before half way in the halfs I've also used the gels to give me a boost when running before breakfast. It's probably a case of getting used to it again, because I don't often run before breakfast, but I've found I struggle with any sort of distance without them.
No downsides that I can think of. Upsides are reduced race fees, free training (ok, covered by membership), social scene, and often you get discounts on kit from local shops. I joined a club earlier this year, and have seen some improvement in my running despite not making down to the track nights every week (probably averaging once every two weeks). I also find it a motivating factor - it's sometimes easier for me to motivate myself to go to a track session than it is to get out and run on my own.