As a whole I agree with LTL that for the average person, the $7500 won't make a big difference in terms of buyers, especially for single vehicle households. However, for those who are in more metro areas, where the $7500 credit comes into play the best is on leases, as it gets the amount due at signing and the monthly payments down usually in the $200/mo range.
Tesla won't be able to tap into these credits after 2017 at the same rate, as they will taper down once certain sales amounts have been reached (200,000). The sad thing about that is, for a Tesla owner, all that $7500 did was allow them to buy additional features, instead of actually being an EV purchase enabler. I personally think that the credit should only apply to vehicles under a certain dollar amount, say $50,000.
The $7500 credit is also a bit of a sham in a way for buyers, as it means instead of the traditional 15%(or so) residual loss that occurs when you drive it off the lot, you can slap an additional $7500 on top of that. That, (combined with battery issues), is among the reasons why Nissan Leafs have such terrible residual/resale values. I mean, how else could I buy a 4 year old car that sold for $37,000 new, and get it for $6,000 when it's in terrific shape? If you add in that $7500 it makes it a $13,000 car which is closer to what I would expect for a vehicle of this age in this condition that had such a starting price.
The upshot of that terribly low residual price is that there are a lot of people who are buying these ultra-cheap Leafs and using them as their commuter vehicles. That's great, in my opinion, but it doesn't really help the original purchaser unless they were doing a lease, or plan on driving the car into the ground and never selling it.
But here's a positive spin on the tax credit thing, if they're eliminated by Congress, people can claim that they raised taxes, which is certainly the antithesis to the Rep platform.
For me, I just plan on touting EVs as much as possible, by giving people rides in it, letting them feel the smoothness, hear the relative quiet, and then tout the fuel savings. I say that once you've gone EV, you don't want to go back to an ICE. (Which on the topic, LTL, are your ICE vehicles holding you over until you can get a 200+ mile EV?)