Fuji Abound you seem to have been a bit unfortunate with your experiences with Luton. I operate from a little grass strip under the approach to 26 so get to talk to Luton Radar a lot! On very few occasions have I heard Luton Radar turn down a transit request, if they are in one of their extremely busy patches ,or there is a new controller on then there will be the standard phrase "remain outside controlled airspace" but it is usually suffixed with an assurance that they will reply soon.
Personally I think Luton are a great example of how mixed GA / CAT should operate. In their immediate surroundings they have two active glider sites, three microlight fields, three grass strips, an RAF light training base (Henlow), a busy GA field (Panshanger) and a field that hosts regular summer airshows (Old Warden). Couple this with the demands of easyJet, Ryanair, Monarch, Whizz plus others and a host of bizjets and helicopters flying into Luton (oops plus the Police helo) they cope remarkably well and provide a couteous service.
PS Forgot the Luton Flying School operating from tha airport itself.