In reply to Ciderslider:
Advances do get slower the better you get but you can keep advancing for a long time if you do it right.
Indoor bouldering is probably the best form of training for climbing there is. It's hard to say how far you will advance because there are so many variables.
I'm a really weak climber when it comes to bouldering but I still got up to V8 (f7bish) just spending by the winter at a good bouldering area (Hueco Tanks) - no structure, just going out and enjoying climbing - though I did a have good base of technique from route climbing to draw on.
I suspect you might be limited by where you climb. I'm guessing the Brighton wall, not being in a popular climbing area, probably caters for lower grade climbers. I've only been once and that was more for the kids so I don't know. Expectations and being surrounded by a lot of very good climbers can make a surprising difference.
If you want to improve your technique I'd say just watch lots and lots of bouldering videos on Vimeo and Youtube of top boulders in action. There are tons of these things. Gradually try to integrate the way they climb into your own climbing.
I don't think there's any point in thinking about how far you can advance because without trying you're never going to know. Expect and plan to get better over time. You're even going to hit plateaus some times but that's OK as long as they don't persist for too long. Once you get a range of ticks at one grade you can start thinking about breaking into the next grade up.
The main things that stop climber's advancing are:
1. They don't push themselves hard enough.
2. Not climbing on a regular enough basis
3. Injury (which leads back to 2)