IU have purchased a dt400 with a vape ignition system  All the wiring has been cut.  I have all the parts to go back to stock and a wiring harness.  Is there any performance reason to go with the vape system other than the stock system is hard to find

This may be an unpopular opinion, but ... Air, Fuel, Spark. I'm guessing the bike was running the desired AFR from the factory. As such, adding /decreasing voltage to maximize spark for performance may not make a difference. If your original system was malfunctioning, then I guess it could help a lot.

I'm adding the VAPE on my 360 now. Goal: reliable spark, good lighting.

Most of the benefit in my opinion is the electrical system...  VAPE has a modern regulator/rectifier but beyond that,  doubling the voltage to 12v cuts the amps the old wire, connectors, and switches have to carry by half...  So the negative effects of high resistance in the old wiring system...  primarily voltage drop...  is reduced by at least half... probably more.

As far as spark, that's one of those things where all you need is "enough".  If you have a good enough spark for reliable ignition, that's all you need.  A more powerful spark than "enough" gives you absolutely nothing.

Points to VAPE has one potential minor benefit...  there is a "natural" timing retard at low RPM with the VAPE which can make starting easier...  some Yamaha points systems have mechanical means to retard timing for starting and all the CDI systems have either the "natural" timing retard or a start retard designed in.

VAPE does not have a variable timing curve but there used to be an aftermarket box for the VAPE that allowed you to dial in advance in midrange and then retard again for high RPM.  Not sure if they are still available.  So with the exception of the "natural" timing retard at low (kick over) RPM, the VAPE does not have an advantage over stock Yamaha points or CDI on these early bikes. 

 

I’ve seen photos of the original Mitsubishi flywheel on a scale next to the Vape flywheel and it’s a pound or a bit more difference, the Vape being that much lighter may well make the Vape 400 rev a little quicker making it feel faster, haven’t fired mine up yet to know if it’s a noticeable difference.