I need advice.


Background: I am a devoted music listener for over 50 years.  Most of my knowledge of technology is from the 70's.  
Objective: The best sound quality I can get from my system.
I have numerous amps, turntables and speakers.  The best of these is as follows:
My audio system;  Thorens TD 160 with Stanton 680EEE cartridge, Sansui AU 717, JBL L112
The Sansui (as far as I can tell) is untouched as far as any refurb is concerned. The overall quality of the audio as far as I can tell is good.  But it is what I listen to every day so I have no source for comparison. I have read that an amp that is 30+ years old is due for refurbishment (new caps, etc.).  I have been quoted $350 - 400 for a total refurbishment of the Sansui 717.  I would consider having this work done if it would make a noticeable improvement in the audio quality.  What  can I expect from such an investment?  I welcome any suggestions.
garywest
I still have my TU-717 tuner, but it's on a shelf, so I have not listened to it in quite some time. I used to own the AU-717 as well. About a year ago, I got stuck without a modern preamp, because I replaced my integrated amp with power amps and could only insert my Boulder L3AE line stage as a temporary solution. The Boulder is only 26 years young as compared to your Sansui of 40 years. Wow, the Boulder sounded good, but after I had a cap explode in my old and untouched Heathkit amp a while back, I decided to replace the caps in my Boulder. After some break-in, the Boulder sounds fantastic and I have no urge to go shopping right now.
Kenny
In addition to electrolytic caps, Tweeter damping fluid or ferrofluid is the other thing that will go with time and use (dries out). Foam surrounds can wear out too. After more than 30 years your electrolytic caps are likely shot or at least out of tolerance - those in the signal path are most critical.

I'd be wary of simply assuming a $350 recap will get you back to original 70's performance. You should try to test your individual components separately A vs B against modern gear.  These age related failures should be fairly obvious - night and day differences. If you find your speakers need a refurb too then the cost/benefit may steer you towards a different solution.
The AU-717 is very capable, but it comes with a laundry list of problems that need to be addressed. I have worked on several of them myself, and they have what is dubbed the "Glue Syndrome". Just google Sansui Glue, and you will see it posted about allot. This stuff eats component leads when it becomes corrosive and even conductive.

The other big issue with the 717  is the filter capacitors are always bad and leaking or starting to leak.

If you can get it completely restored for $350, you better jump on that deal, because I wouldn't do what I do to them for that. I remove all the glue, and replace all offended components. More to it than that, but the glue issue must be dealt with.
Garywest ...

I love that turntable .. very musical. 

You're a music lover first and not an equipment geek. Keep the Sansui as a spare and go with tubes.  It doesn't have to be really expensive. Check out the modified Dyna 70's. Maybe a modified Dyna Pas pre-amp as well. 

Find out how to contact "Grover."  He builds excellent Dyna 70's.  A friend has one and its pretty amazing. I don't have his contact number, but someone here may chime in. 

OP
The 717 was a great product for its time. If i was on a budget I would recap using really good caps, Jensen, Mundorf or something equivalent.  If you are open to spending some $$$, there are some fantastic newer products in integrated. Before i purchased my current separates, i was very happy with a BAT vk 3000se. There are some other fine choices available for less.