As was mentioned, it's not the amount that you owe or get refunded when you file (line 75 or 78 on the 2015 1040 tax form). The critical line for being able to claim the full EV tax credit is your total tax (line 63 on the 2015 1040 tax form). If that is at least $7,500, you can claim the whole credit.
Personally, I wouldn't make any major changes to your tax situation on the expectation of getting a Model 3 delivery in 2017. I did a Mar 31 reservation, but doubt I'll receive mine until 2018 (and may push back on the first offer to configure since the closest Tesla Service Center is a 3 hour drive away).
Looking at total tax (line 63) on your recent 1040 tax forms, if that is not consistently at $7,500, the one thing that I would consider doing would be a Traditional IRA to Roth IRA conversion in December 2017 to artificially inflate your income for 2017. The logic being that if you were only going to be able to claim a partial tax credit for the EV purchase, by doing an IRA conversion, you get to the conversion to go through (and don't pay taxes in the future when you withdraw the money or now when you do the actual conversion. For example, if you typically had a total tax (line 63) of $5,000 in recent years, I'd convert between $7,000 and $10,000 from a Traditional IRA to a Roth IRA in the year that I made an EV purchase. This would add to your income for that year and end up and increase your total tax by $2,000 to $3,500, putting you at the point that you could claim the whole EV tax credit.
This is something you could do very late in December once you had guaranteed that you had completed the EV purchase. If you didn't have the EV purchase to absorb this extra tax liability, the tax on the conversion would need to be paid out of pocket.