Sometimes my idle can be floaty and flares a bit after warm restarts. Can the base idle setting being too high cause this guys?

A high base idle would more likely result in a constant high idle as the base idle is the theoretical minimum RPM the engine can operate at. Hunting idle/flaring on restart more likely an ISC condition or a vacuum leak (isc = computer controlled vacuum leak).

Thanks mate. That's what I thought. I had a couple of things done to the car yesterday, including a new thermo housing, old one was pitted and draining coolant at a very low rate, but he turned down my idle slightly, which if I know my car, is now a bit too low. She rumbles and vibtrates when the rpm goes down when pulling up to lights.
There shouldn't be anything wrong with increasing the idle screw without putting the ECU into diagnostic mode should there, I might do it before work this morning?

Yeah more likely a sypmtom of a base idle that is set too low. EEC is constantly interfering with the base idle via the ISC - and can tend to overcompensate, resulting in reasonable increases in RPM.

I'd recommend disconnecting the ISC prior to adjusting the base idle.