1) Yes I know Heathrow Express is a rip off!
2) Yes I know the journey is only 15 minutes
3) No, I don't know what extras you can get with first class.
But I hope some people may find this useful. Just click on the link, fill in your details and hey presto, you get a code which you can use to upgrade your standard tickets to first class.
I am going on a business trip so will be taking advantage of this offer. Hope it helps anyone else out there.