Should I invest the time to build Google+ circles knowing that I will want to eventually use my Google Apps profile when it's supported?

I would keep your personal and work profiles separate.  Use your personal account for your main personal, non work related communications with friends and family and keep your work profile interactions work related.  Create work circles for interacting with other employees about work.

If you are using google apps for personal use and you prefer your apps account for your personal communications over your generic @gmail.com account, i'd hold off.  Merging accounts may be a feature later, or not. Wait and see. Or you can export all your data later if you don't want to wait. :)

Also realize, if you are an employee of a company using Google Apps, your work profile belongs to that company.  You will likely see warnings that the google account you are using is the property of the domain.   Heed them.

When leaving a company, you leave your account and all the communications you posted behind. The apps account will likely be renamed and given to the person taking your place.

Keep your work and personal life separate if you can.  It's what a professional would do. Your family and your collegues will respect that.