Well, usually reapplicants have something to prove because they want to see how you've improved since your previous application. If you really feel you've made no improvement, and you could make significant improvement by R3, then it might actually be better for you to wait. But I have to admit, its hard for me to imagine how much a few months could really make in your application. With a 630, you've got to bring something special to the table, so I'd do everything you can to boost other aspects of your application. For every 630 they accept they need to admit (and yield) two applicants signficantly above 700 to keep their average. You need to show them why they want you over another applicant with similar stats.
Booth is a top 10 school, and they reject a lot of applicants. If your application didn't get you in previously, and not much has changed, I would do my best to add as many "new" aspects to it so you can discuss that in your reapplicant essay. If you send in a R2 app, with no changes, and maybe no rec letters, I think your setting yourself up for failure.
I would do my best to get a 680+ GMAT to show improviement, I would work to get amazing recommendation letters, I would get involved in your new EC so you can have something to speak about, I would work towards (or request) a raise or promotion. Even getting that new job, and some experience there under your belt could help in the discussion.
It is usually not advised to submit R3 over R2, but this may be the only time its acceptable. You have a lot of work to do, to really show that Booth is the school for you. Put 110% in, so atleast when you look back in 10 years, you know you did EVERYTHING you could to get into your top choice. Good luck!
Are you applying to other schools also?
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