Windrusher, a few points from my experience for what it's worth.
" . . . should I really distract myself and everyone else with ropey courtesy calls when I'm near controlled airspace? If so, how near and how often?"
I listen (usually Essex Radar, as I did today for 1 1/2 hours) for conflicting traffic. I don't call them unless either I want to go into CAS (as one can request for Stansted's class G), or they seem to be working someone who is heading my way. Last time I did the latter, as I noted above, they didn't want to know. When I have requested clearance to enter, I had no actual refusals but some less than helpful clearances (e.g. "not above 2000 feet QNH" - a recipe for landing out. Which I did.) Other airports have been less problematical - e.g cleared through eastern end of E Midlands, OK to land at Yeovil.
Practice saying what you need to (for a position report and the service you want). Listen to the spamcans doing it - you can hardly make a worse mess than a few of them do, but if you copy the best you will be accepted as OK to talk to ATC. NEVER go into CAS until you have established contact and have permission - asking afterwards is asking for a prosecution. Park in a thermal if necessary. Don't expect to keep up your average X-counrty speed while negotiating CAS.
" . . .if we're all to call in updates every ten miles or so, what'll happen . . .?"
They don't do it like that. When they call to ask your present position and height, just tell them. I often use the phrase "manouevring to gain height 2 miles north west of Ytown, climbing through xx00 feet" or whatever, when thermalling. Alternatively, if they ask you to report when reaching some height or some position, say "Will report when reaching xtown [or xx00 feet]". Listen to how others close off each transmission and copy. It's often in the form "glider XY" rather than "over". When leaving the area, again copy what others do, but typically I use "XX radar, leaving your area to the east, thanks for your help, QSY gliding frequency 130 decimal 4, glider XY". They acknowledge and thank, and that's it.
"And how well DO we show up on radar, by the way? "
Varies from mediocre to badly, but it's not your problem so don't worry. They may ask you to confirm your track - "Glider XY ,are you still tracking west?", or do a turn e.g. left, for corroboration of where they think you are, but not usually.