David, The main benefit is probably access to the events. Between Green Road Runs, Tyros, Driving days, Fun days and on up into the more competitive stuff there is something for everyone from kids and beginners to serious rally nuts. Probably the only bit we are currently lacking as a Club is much activity in the classic car/showing/restoration area - but if someone wants to run with it.....
Other benefits are that some places give Discounts to SLROC members and it can help with some Insurance companies too.
This is a public forum and great for tech questions and sales/wants - but a bit of face to face networking out on some wet hillside with other Club members can pay dividends in terms of help from mates when problems arise etc.
You get to read about youself in the newsletter - especially if you do something daft on a hill - and there are some good social events and fun-days. You get to be a member of a Club with a bit of history, able to wave at fellow members LRs when you see the sticker in the window etc... For the price if a 1/3 a tank of Diesel its good value !