I think the OP has got the terms wrong. I don't think you Flare a glider into a landing. I think you roundout and then just hold it off until it lands itself.
I think Flaring is something you do in a C-172. Or most power airplane. If you try and flare a glider your likely to hit the tailboom hard and / or pound in. Tailboom first landings are the way the euro's try and land, but Flaring? I don't think so.
Am I wrong?
I think any pilot going XC should be able to spot land his glider with full Spoilers out and flaps too if you have them.
I don't know of any glider that can't be landed with everything hanging out to the max but I'm sure someone here will correct me on that point. My ASW20 was and my LS3a is, easy to land with everything out to the max. It is good to practice this a couple of times a year in good conditions thou.