Man.
That depends.
First thing: does the "Old Vaq" fit your hands? That's the BIG question. If it does, then get another and be done with it.
Do "the checkout" first though, as build quality with the New Vaq is a bit higher on average than the "Old Vaq". The New Vaq is consistently one of the best guns Ruger has ever made.
The New Vaq is a "size clone" of the Colt SAA. The innards are way different but the feel/heft is close. The New Vaq is a better fit for the 357Mag cartridge, as it's pretty much the perfect size for that round. The Old Vaq was built on a 44Magnum-class frame. Both guns can handle all factory 357 rounds (including the wildest stuff Buffalo Bore and Doubletap make, up to 800ft/lbs energy which I've shot out of my New Vaq 357). The advantage with the Old Vaq is you can safely rechamber it bigger later if you want...not a factor in CAS/SASS of course. And if you're a reloader, esp. a newbie reloader, you might take comfort in the fact that the Old Vaq in 357 is among the world's strongest guns in that caliber and more tolerant than most of *minor* reloading errors. You can blow one up, but it takes a major screwup to do so.
And...that's about it, really.
If you like the New Vaq's feel, you can probably unload your current gun for a good enough price to mostly pay for a second New Vaq. Maybe do an even trade with a bit of luck and finding the right buyer looking for the Old Vaq for some reason. While out of production there were enough made that they're still "shooters" rather than safe queens so...you might have to toss a bit of cash into the trade. Shouldn't be too bad though.
What else...do you shoot your SAs "pinkie under" the grip? If so you're more likely to dig the feel of the New Vaq. That's how I shoot and I absolutely love mine...I CCW the dang thing
.