Whats my Nautique Worth?

I would say $5K to $7,500 maybe.   Good luck with the sale.

My first ski nautique came from a private lake, the seller never registered the trailer or boat for 15 years.

He had to title it, pay taxes and overnight me the signed title once he got it so i could register it.
I also had to bring receipts for steel and trailer parts to get the correct craft trailer registered as homemade because he had no paperwork or bogus from the seller he bought it from paperwork which did me no good.

Luckily he did that or the boat and trailer would have been scrap.

You guys who never title/register your boat and trailer aren't gaining anything or saving any money.

If the dmv wants something from the seller you got it from good luck, the hull is a worthless yard ornament or dump it on an off ramp somewhere.
maybe 500 bucks for the engine trans running gear windshield, maybe !
The trailer is worth 100 bucks because it's 39 years old with no title or registration and no one wants it and you can't sell it as a correct craft model 3 in someone elses name, or yours cuz you never registered it.

If it runs and doesn't need a thousand bucks of tune up belts hoses prop shaft, strut bearings etc etc and why would it need that because everyone performs maintenance right before they sell a boat then it's worth 1500 bucks to someone on your lake who will never register it or ever need paperwork / or you could lie and sell it (looking for the title) to someone / or you can part it out, i.e. dis assemble and store every piece and part for years until each piece has been sold boxed and shipped 1 piece at a time, except the hull because the dump won't take it without a title and with all the cameras you'll get caught dumping it on the road, the tracks or down a boat ramp.
Or it's worth 600 bucks no title parts only as is get it outta here with only a hand written bill of sale which legally means jack-sh*t because you beat the system by never registering it in your name and then that's only if someone can get rid of the hull and wants the parts.

Good luck with the sale.

Edit in another 50 bucks because i see it's a prop gaurd trailer. 650 bucks.

I had not ever faced the no title issue.  I did buy a 1978 that was stolen, used for 2 years and then recovered.  I received paperwork showing all proper numbers from the insurance company and got the boat registered in my name.  Several years later we painted the trailer and found the numbers on the trailer did not match the paperwork I received so the crooks stole a trailer and then stole a boat from different places.   They also ground the serial number off the rear of the Nautique so no way to know if it was really the boat that matched the paperwork.   It was stolen in Reno NV and recovered near Napa CA.   I had it about 8 years sold it in 1990.

Sounds like an easy fix and good paper trail to the owners.  Nothing wrong with that.