Rangefinder vs. SLR. Very different shooting styles. If you haven't tried a rangefinder, I'd probably start with a less-expensive fixed-lens model and see if you like it. No reason to buy a camera that you don't enjoy.
As for Zeiss vs. Nikon, I believe many of the Nikon lenses were based on Zeiss designs. Or at least they were "way back when" ... before zooms and the (over)emphasis on high-speed optics. Anyway, I'm getting way off track.
I agree that there is a difference in the results from the two groups of lenses, although the differences narrow at smaller apertures.
And then there's Leica -- also a top-shelf maker of lenses and cameras for both rangefinder and SLRs. But they will most assuredly blow past your $1,500 budget.
Comet, if you haven't decided on which way to go here is my two cents:
1.) Get your F3 repaired by a reputable repair shop if you like the camera. There are several people here who can recommend their favorite Nikon repair guy who will actually fix the camera.
2.) Since you have some Nikon lenses, it would be much easier on the pocket book to stick with a Nikon body. If you like the F3 style of operation, get another F3 or variation (as stated earier, get it from a reputable dealer such as KEH....NOT eBay).
3.) Consider an FE or possibly an FA.
When you say you can't get much "crispness" out of your setup, are you saying you are having problems focusing? Perhaps you need to leave the manual focus cameras in the past and consider a autofocus Nikon camera. I started with an F4S and now love my F5. With a TC-16A, you can have autofocus with your old manual focus lenses. I can't tell you how much the built in diopter (in both the F4 and F5) allowed me to fine tune the finder for my failing eye sight as I get older.
No need to blow alot of money in these economic times.