Nothing against barrow farm as I enjoyed it when I was there, but the way you described street sounds pretty fun to me, except replace "wall" with "really cool random shit" (cos London's architecture is pretty nuts). Riding to and from locations is all part of the fun of riding. Plus there is the finding a way to get over something that wasn't designed to be ridden that I find really appealing. Trials parks are "designed" to be ridden, but the problem solving of riding street just can't be beaten (Natural is pretty close though).
I do see both of your points though, it's like when I see videos of BMX park riders who travel abroad just to ride an indoor skatepark.......what's the point in that? ramps are all pretty much the same (just different layouts, but a fair on a quarter is still a flair on a quarter) You don't get to see the local way of life, see the sights, smell the smells and find new things to ride like you do when street riding. On the other hand, trials parks are not quite as predictable as skateparks, so they can offer a different experience from other trials parks.