There will be no doubling of price in December; that event is already priced in.
That only factors in speculators. Real users of BTC will only care about dumping all their fiat into BTC and sending it to someone who may then convert it back to fiat.
If such real use is a major part of BTC now due things like SR, then a doubling might not be priced in at all before the halving.
If I had spare cash I would still buy in now, but I wouldn't be too surprised to loose on the short term with value going down to 5.5 or so during the summer.
You're right that it's speculators who are setting the price. But wrong that the second group has any effect on price.
Buy X -> Transmit -> Sell X
Would not change the price at all, since for every bit of demand created by "buy X" an identical and opposite supply for "sell X" is created.
The thing that drives the price is holdings, call them speculators if you want, but as time goes by and the price of bitcoin becomes less and less volatile, people who are not speculators effectively become speculators -- because the risk is lower -- and increase demand. This process certainly won't be triggered by the halving of the block reward.
None of which changes the fact that the block rate halving is unlikely to affect the price in any observable way. The only people it will affect are the miners. Half of whom might switch their rigs off.