New Tri Bike vs Aero Wheels on Road Bike

$2500 for wheels is a bit excessive... you can easily save $1000 and still get a great set of slightly used wheels...

You need to look at your needs, type of riding, etc. answer what makes the most sense for you... Are you going to use the wheels in road races, but only do a handful to TT's or tri's each year, then obviously wheels makes much more sense. If you plan to do lots of TT's and tri's, but don't have use for the wheels in mass-start races, then the Shiv makes sense. Just a very important note though... the Shiv by itself won't make you any faster.... it's the position of the rider that makes you faster, so if you decide to go this route, get a bike fit to make sure that Shiv is actually the right bike for you.

If you haven't had a bike fit, spend $1500 of wheels, $2-300 on a bike fit and the rest in the bank (or spend it on some fun stuff, whatever floats your boat). You'll be faster with a well-fitting road bike then you will ever be on an ill-fitting super aero tri bike.

well... no, not that simple... You can't really buy additional speed that way. You may very well be faster on a tri bike due to the position a fitter can put you in (basically the perfect compromise between aerodynamics, efficiency and comfort based upon your limiters, goals, etc.) even if you are using standard box rims. But if you buy the wrong tri bike and you simply can't get efficient and aerodynamic and comfortable, then yes, you will be faster on a road bike given that is fitting you well...

Wheel cover rear and generic chinese front wheel.  All the aero you need for wheels for about $350.  Spend the rest on a decent tri frame.