I don't think Singapore will be able to afford the UCAV on a
large scale basis to have any significant impact in its armed
forces. It would more likely use UAVs for recon etc. Also,
Singapore does require a large number of UAVs. UAVs are lost or
written off VERY easily. Probably 'cos they're harder to control,
especially if you lose contact with it, although current SIngapore
UAVs are programmed to return on their own if contact is lost, but
it is still very easy to lose a UAV. Another reason is that very
often, you need continuous info of your enemy/battlefield. To do
that, basically you need a large number of UAVs (some sending
feedback, some on their way/returning, some on standby and some in
maintenance)
also, I doubt it necessary for a supersonic UAV. A UAV should be
stealthy. If the enemy find your UAV, you can say byebye to it
already, 'cos most fighters today are supersonic and SAMs are even
more so. (unless the enemy has yet to scramble planes and does not
have SAMs aimed at you, which is highly unlikely once the UAV is
found) Once you're UAV is found in that sector, most likely you
cannot put anymore UAVs around there because the enemy will be on
their guard there, so the best option is still to be stealthy and
not speedy.
A UAV also beats a satellite in that you need several satellies up
just to ensure that you can give 24hr coverage of the enemy(at
least 3 sats i think). Otherwise, you'll only have info when the
your sat is overhead the enemy. A UAV is there when you need
it.