PE - if you can afford the extra cash - is definately worth it, especially in the bubble. Unfortunately the LGW/MAN fleet has yet to be upgraded with the new PE cabins but even though it looks and feels rather tired the seats are much bigger than economy, the food served nicely, dedicated cabin staff for a much smaller amount of people, and when you're in the bubble feels like you're in a small plane all on your own! You also get Priority fastpass for security, suppposedly priority luggage offload (that ones not always true!) and priority boarding ahead of economy.
As for the clubhouse only those with a UC ticket or Gold Flyer card get in automatically, you can pay to get in if there is space, try the Virgin Holidays site to pay for it. Its definately worth it too - we always use the lounge (we have a gold flying club card) so always get in, the food is great, seats are very comfy, lots of staff around heling you with everything, the fact that you have great views, makes the airport experience somewhat nicer! plus you only get called for the flight right at the last minute so dont have to wait for ages in the departure zone by the gate.
Although I have heard not yet confirmed by Virgin, that the clubhouse is closing for refurbishments in Sept for up to 3 months

just when we would be using it!
We tend to fly night flights UC and day flights PE as with the kids in UC on a day flight we've actually found it not worth the cash as they tend to annoy the other passengers walking up and down between all our seats. Just makes us feel uncomfortable in the end. Night flights - we always do UC for the beds!