Andrew, thank for sharing your TIM experience. I hear you and agree with much of what you have to say..
TIM is a strong tool but needs to be baked into the process and there are huge benefits when you move the trade appraisal towards to the beginning of the sales process. . Customers should be using TIM to appraise their own vehicles at the dealership. I would encourage the dealership to build out a TIM Kiosk - this helps reinforce it as being a 3rd party service. The appraisal number is NOT your number but the number from AutoTrader.
Could you elaborate on the "huge time investment"? I have heard this a few times across my sales force. I remind them - documentation reduces negotiation. Let's admit, we spend a lot of time (LOST TIME) in the negotiation process. So time spent on TIM could be saved in the negotiation process.
As for the leads - it sounds like you were a buying center. If this is the case - dealers need to remember they are a buying center this is service is for buying cars and not so much for selling them another car.
TIM Leads from your website VS using KBB or BlackBook or GetAutoAppraise - no advantage there. I would allow the customer to choose between the 2 on your website while reinforcing each with a video to better explain each service. Now that can be a time suck! 
From the sounds of it - saying it's an expensive solution I would guess you are on the Buying Center package.
In the end, I'm a firm believe in this product.
