About all I can offer, Steve, is that I've used the HW-17 for almost 20 years and I've enjoyed the added convenience it offers. Now I use it with Disc Doctor fluid and Disc Doctor brush (with manual scrub), but I continue to use the -17's fluid applicator to apply the distilled water rinse and then vacuum. My cleaning results have never been better, and the convenience of the HW-17 makes the application and rinse process a breeze. (Of course, many people are doing similarly with the HW-16.5 and find that combination very successful, just have a somewhat messier rinse process.)
The only change in the model over the years, as best I understand, has been the introduction of the fan to keep the motor cooler (the HW-17F). I have the original version without the fan and it works great, even after all these years. Without the fan, you just have to limit your cleaning to about a dozen records per session. I'm sure a fan can be added to my older unit, I've just never felt the compelling need, and I've used it across literally thousands of records.
Is it worth upgrading? Dunno. I think it depends on how many records you're continuing to add to your collection each month and what cleaning regimen you've chosen to adopt. I certainly wouldn't trade my HW-17 for anything else now that I have it.