The annoying thing is that 10 years ago, before the onset of the Lo-Cos, these airports were MORE than happy to host us and let us visit. This is the bit that sticks more than anything. A case of playground "rules", yes I will play with you until someone with a bigger packet of sweets appears.
All that said, as opposed to most of the aforementioned airfields, Manchester IS an International airport and is not struggling for an identiity, it always has been a leading light in the regional airport business, even if there are problems but that is for another forum! As GA we can still visit today. I think the landing / handling fees are about £30 or £35 through MSF, which although more than a tenner at say Sandtoft, is not bad value when you get the opportunity to put it in your log book, and have the attractions like Concorde on site and get to enjoy all the same "aids" as the bus drivers. The ATC guys are in the main "old school" and will help you where they can as long as you aren't a total muppet!
Might not be a destination of regular choice, but there are challenges in flying there and for a "different" place to go it has to be worth a try now and again!