Some flapped gliders benefit from using 0 or negative flap during the
initial part of the takeoff, a slightly higher pilot load.
Dumping or retracting flap in the late part of a landing can result in
a rapid loss of lift and resultant heavy or worse 'arrivals'.
Most gliders spin / stall charecteristics change depending on flap
setting.
Spin recovery procedure may involve flap setting.

Now what will another 1, 2 or 500 hours in unflapped gliders teach you
about all of that? Very little if anything but it may make your CFI
more confident in your workload handling capacity.
My suggestion, get some dual time, a couple of hours at least, in a
flapped 2 seater, ( IS28, Janus, Nimbus 3d whatever ) and then get the
instructor to give you an honest assesment of YOUR capabilities.

Some pilots can handle the load with 30 hours, some with a hundred
hours and some pilots are so far behind the aircraft they never will.
Its your personal capabilities that matter, there is no prescribed
point in a logbook that suddenly makes you capable of something.

Ian