In the long run, all government debt is going to be future taxes. There are many programs that the government spends on that are efficient and produce more growth than the taxes collected would have, and there are many that don't and produce less growth than leaving the money in the hands of the taxed. Sometimes this is due to government inefficiency, and sometimes because we decided it's what we want, like medicare for elderly who will never return the investment into their health.
I'm pretty heavy against "efficient" as a goal to look for in government spending. In particular, the first spend on anything will never be as efficient as later spending. That just isn't how it works. So, if you are trying to seed something with government spend, expect some inefficiencies.
