Quad have always had a reputation for low cost when it comes to servicing and repairs. Considering most 'normal' places would charge a good £30 per hour, £48 fixed cost seems incredibly reasonable. Of course, it depends on parts costs, but I'd still expect that not to break the bank.
Yes you could. But the panels and the EHT supply, which are the two things most likely to need attention, will almost certainly count as replacement parts. Actually fitting them doesn't take too long if you know what you're doing. But the parts themselves may well not be cheap (they wouldn't be wherever you bought them from).
Also I think it's fair to say that Quad do a super job on functionality. They set the specs and they will make sure that your kit is meeting them when you get it back. But in times past, at least, they didn't include anything at all cosmetic in a service. Sprucing up doesn't affect the sound, so it's an optional luxury not a necessity.
I can highly recommend Quad servicing. I have had a few 405's and easily the best sounding one was a late 405-2 serviced and recapped by Quad. You can even get them to supply new packaging with nice foam padding to protect your new (old) for components (not sure if they do same for speakers)