Rental cars are very inexpensive in Vegas and Tahitti village is out near the airport, several miles from the start of "The Strip".
Actually, I believe it's only 2 miles south of Mandalay Bay rather than several miles. Still MB is the far south end of the strip.
As others have mentioned, a car should make your life easier. You can come and go as you please without having to follow a shuttle bus schedule. Getting back using by taxi might be easier than getting to the strip by taxi. That's because there's always taxi lines at the casino's but getting one called down to TV could be difficult unless one just happens to be in that area. Taxi drivers don't like dead end fares where they can't pick someone up when they drop someone off. They prefer to stay around the hotels where there's always someone waiting to be picked up once they've dropped their last fare off. They're not into driving an empty cab 2 miles south of the strip to pick someone up to drop back off on the strip.
Keep in mind that taxi's in Vegas are amoung the highest in the country as far as fare's go. They might seem reasonable to most because most never really go that far but, they're not cheap IMO. You can easily spend more than a rental car would cost you in cab fare's in the period of one week.
The shuttle bus is nice because it's free. Once on the strip you probably won't need a car much. The problem with a shuttle bus is you have to follow it's schedule. If everyone at TV is utilizing the shuttle, then you could have to stand and wait for the next run if the shuttle is full (never heard of that happening). I'm not a big fan of having to be standing and waiting based on a shuttle bus schedule so I prefer to have the car.
If it were me, I'd get the car.