Speaking as a local there are a few places to fly....
Watergate - great beach, great kite school, but in the summer lots of kites, dog walkers, children and trainee buggy pilots (not a citisism, just an observation) add in a large surfing community, kite surfers and you get the picyture, really good place for early evening low tides and NW winds.
Perranporth - about 8 miles from Newquay (head west and follow the coast road) 3 miles of beach loads of room, the public tend to mainly be down the west end of the beach, soft sand at high tides, but nice beach at low tides (for buggies), great scudding at mid-high tides.
Gwithian - about 25 miles west of Newquay, great beach miles and miles loads of buggies but it never seems really crowded, firm sand - what can I say - that's where I go for a good buggy session.
There are other beaches, but that's about the top 3 IMHO.
HTH
Bowcaps