Here is an idea you might enjoy, which has no actual affect on the gameplay, but which will increase the pace at which players play. This will work better in my view than any kind of carrot or stick or timer. It exploits a game flow tendency that many players exhibit regarding the purchase new units phase.
Basically you alter the game phase sequence to the following…
Research/Repair
Combat Movement
Purchase
Roll Combat
Non Com
Place
Notice that all you have done is to insert the Purchase phase between the Combat move, and the actual Combat roll.
Effectively you reverse the order of purchase and combat movement…
from Purchase/Combat Movement/Combat Roll
to the much speedier Combat Movement/Purchase/Combat roll.
This does not affect the gameplay, it doesn’t change any of the results or information available to you, but it does do several something important things… First it puts your mind in a different place at the beginning of the turn.
It focuses the player’s attention on the combat moves first and allows them to concentrate on all their attack movements immediately with no distractions about what you just bought. Then, once those movements are determined, the player makes their purchasing decision. They will purchase much faster now, because their movement decisions will suggest evident purchasing ideas to them, and they are less likely to make stupid purchases. Or to make purchases, then forget why they bought that stuff, and do a bunch of silly moves. Finally, because Purchase happens between the Combat Movement phase, and the actual Combat, it makes waffling around or backing out of your combat decisions less likely.
Basically, once you buy, your combat moves are considered set, and can’t be altered. Think of it like this, combat move, pause to consider purchase, then roll the combats. This does something in the game flow, that really does seem to encourage a more rapid pace.
Combat move guides the purchase, but it doesn’t have an effect on what the rolls will be. For example, you aren’t getting to choose your purchases based on the results of the combat, Purchase phase still occurs before the Combat Roll phase proper. Basically you are just interjecting it between Combat Movement, and Combat Roll. Which has no substantive consequences, just makes a formal change that streamlines the decision making process.
Very simple, but it will increase the speed at which your players make purchasing decisions, and will encourage them to make better purchasing decisions, and to stick to those decisions once made. I’m not sure who first innovated this concept, but it was introduced to me by players on tripleA, and it did definitely speed things up.