Let me help you with this. ALL pay plans should reward the behavior you want the employee to do. If you don't want the technicians upselling, don't pay them for it. If you want them to do it, then you should pay them for it.
I once worked for a company that wanted customer profiles on every company we called on, and paid $100 per profile filled out. As a salesperson I was techically supposed to sell products, but I realized very quickly that I could make more money filling out profiles than selling products. My sales quickly went down, but I had some beautifully filled out profiles. The company knew everything there was to know about the customers, but we didn't sell squat. Let that sink in.
So yes, but with the salespeople's knowledge. Often a tech can get the customer to upgrade the number of smokes, the number of motions, etc., sometimes even upgrade the panel to one with touch screen or remote software. The technician is looked upon as the expert, the salesperson is just that, someone who is in it to sell it. Not all technicians can sell, and not all salespeople can install. The ones who can sell should be rewarded, but the technicians that can't may be rewarded because they install more efficiently, have fewer call backs, lose less inventory or tools, or any other behavior that you choose to motivate for.
Everyone, even the company owner, should have some sort of commission or bonus plan, preferably tied to profit. After all, if it's not generating a profit, is it really desirable behavior? That's what we teach in our alarm business class.