Do you improve more as a writer by revising your 1st draft or by writing a second novel?

It's universally acknowledged that to improve as a writer, you need to write more! Fine, but my question is:

Do you improve more just by writing more, or do you really need to be critiqued by Beta Readers and go back and rewrite and re-edit before moving on with the next novel?

Right now I have written two novels. One is a 1st draft. The other is a self-edited, 2nd draft with no Beta Reader critique. I want to write two more novels, and if I just focus on writing the new novels, I'll probably finish them in about a year. Is it advisable to write new manuscripts without receiving feedback on and revising old manuscripts first?

At the moment I have a low paying but low stress job which allows me time to daydream and write. In the future, I may take a higher paid, higher stress job, which would likely kill my writing for the duration that I work there (maybe a few years?). I'm figuring that if I have 4 basic manuscripts written, then stop writing for a few years, then I'm more likely to go back and revise the already written manuscripts once I get more free time. If I spend my time on revisions, I'll have two completed books which are better quality, but then I'm less likely to ever write the other books.

Thoughts?