Is iZotope's RX4 Advanced the best/fastest way to clean up/reuse old performances on tape?

The short answer to your question is "yes." 

Thanks for your responses, Craig and Don.  Much appreciated!
 
Don, the "hours" reference in my background was a little faulty.  I should have said 3 hours of songs, each with multiple vocal and/or guitar tracks.  I should have used a multiplier.  :)   Having someone else do this audio cleanup for me is still an intriguing idea.  Thanks for suggesting that.

How functional is the RX4 10-day free trial?

I downloaded the trial of RX4 Advanced and it's fully functional from what I can tell.  You just can't save any of your work.  
 
It seems extremely powerful, allowing for detailed/high-quality surgery on my audio files.  There is a learning (for me), but playing around with the trial version and watching youtube videos on various applications of the tool has been quite helpful.
 
I just need to upgrade my Work Life (standard edition) to the Retirement (full version) in order to free up more time for this most enjoyable hobby.  :)

Another option is Adobe Audition. I believe their trial is fully functional for 30 days, but cannot remember (and possibly changed). I have Audition 4.0 (from CS 5.5) and had CC for the trial, but only used Flash/Dreamweaver for that period (I was allowed to save with both programs, about 2 years ago now).
 
The noise reduction tool is pretty straightforward. You just need a half second or so of background noise to capture as a noise print, then remove it from the track. You need to select a region to capture, and once captured, just click the track to deselect that specific region and remove the noise print from the entire track. I have rarely had to go beyond this (default Adobe settings), but can run it more than once, or even tweak it quite a bit.
 
The de-reverb tool requires a bit more finesse and does not yield perfect results, but can be quite good depending on what you are working with and how deep in the mix that track will end up. The best results are if you can give it a good clue for what it is seeking (i.e. a close proximity of the original reverb settings).
 
As you can set a sonogram view in tandem with the waveform display, it makes editing out pops/clicks a lot simpler and also has an "autoheal" tool that when used on the sonogram view is quite effective. (There is a declick function, but this is not the best choice as it is automated and can easily miss things).

Yet another option is the Magix stuff: http://www.magix.com/us/audio-cleaning-lab/
I don't own these but have used their other stuff which has some of these features and someone here (forgot who) recommended it before.
 
Or, maybe you can loop back the digital io on the scarlett with RX..