I'm a member at the upper level, here are my pros and cons:
Pro: 5c off per litre in Topaz/Circle K
Con: You have to sign up to a fuel card account with them which bills your account by direct debit. Also Circle K and Topaz tend to be more expensive than Applegreen anyway.....
Pro: Free top level car wash with Topaz/Circle K once a month.
Con: Its a brush wash, i'd never take a nice car through one of those. Fine for my X5 hack though.
Pro: Free BMW mini-valet once a month.
Con: You have to book it in with your local dealer which for me (Frank Keane Blackrock) meant waiting three weeks. Then they wont confirm a time slot so you can be waiting around the dealer for hours. The first one I got was also really poor, they never dried the car with a chamois and missed lots of ingrained dirt. You would get a better job at one of those dodgy side of the road washes for a tenner.
Pro: Free Bulbs. There is no con here, if you need a Xenon headlight bulb you get it, fitted and all. I havent needed one of those yet but they replaced a reg plate bulb while I waited.
Pro: Discount on parts and lifestyle from main dealer - you can probably negotiate that yourself but its good to know its guaranteed.
Overall I definitely think it is worth it and I have heard that there will also be some form of loyalty events maybe launches or something like that for members. I recommend it to anyone and I think the Black Friday promo gives 3 months free which is nice!