if I buy an ultrasonic cleaner for my records will I be able to hear the difference?

+1 pbnaudio
i have the same set up. It’s made 40 year old lps, that I took great care of from day one, come to life. Who knew what micro dirt could take out of the music?
amazing
flea market records can still disappoint, but not nearly as often. Makes taking a chance on a $5 copy of Europe ‘72 a good gamble. 
Takes a bit of work to do it right but you only need to do it to disk once. And a good anti-static brush is all you’ll need.  
You’ll find an excellent formula for the bath here on Audiogon, Audiokarma or several other sources. It takes a bit more than just distilled water to get it right. Go for it.

I've heard of "clubs" forming to purchase and share the high end cleaners.  You pool your money, purchase the unit, and each "member" uses it for a week/month then sends it to the next person.

No question it will work. I bought the cleaner vinyl adapter and ultrasonic cleaner about 6 months ago...cleaned all of my several hundred records. It made a notable difference.  They play much quieter, surface noise was greatly reduced. I figure I spent about 300 for the adapter (2 record version) plus ultrasonic unit.  I used a very small amount of Dawn plus photo flo in distilled water.

My first record cleaning machine was KAB's version of the Nitty Gritty. When my friend bought a Keith Monks machine he gave me (!) his VPI 16.5. I have cleaned records using all three of these and have found that when used properly there is no difference in sound between them. All produced clean, quiet records. If you purchase a lot of cruddy used vinyl, an ultrasonic unit just might be better. The more money you spend, the more the machine will do for you.  

YES.   US cleaning will not magically repair damaged discs, but will likely make the sonic damage less audible.

I previously used a Spin Clean and Nitty Gritty---essentially a 2 step version of the VPI process.  I was mostly happy with my results.  Then I spent time to research US theory, process and application.

Purchased a DIY US kit.   Chinese tank, Vinyl Stacker, Rushton's formula.

My results are much better.  Surfaces (including from previously cleaned LPs) are more quiet.  I hear better reproduction of transients and ambiance cues- the the small and subtle sounds that can be buried underneath even moderate surface noise.

Before US cleaning, I still heard a low level   shhhhhhh-wooosh sound on many LPs.  After US, just about all gone.  My take is that a microscopic layer of debris becomes bonded to the LP surface over time.  The layer is thick enough to blunt transients and cover the very low level background cues in the mix.  US cleaning removes this layer, uncovering all that is in the groove to hear.

My cost was about $500.   New Kirmuss machine is about $8-900 and is a self contained box.  Other one box solutions are more expensive.