Hey NCLinda, where in NC are you from? I'm in Summerfield.
Synonymous, it's almost always more efficient to plan your tour around wait times than around using FP, especially for comprehensive tours of the Magic Kingdom. There are certainly instances, such as the "ride Space Mountain twice" scenario you describe, where FASTPASS makes obvious sense. But as a general rule of park touring, I think my original comments are accurate.
One possible explanation for this is that there are many more non-FASTPASS attractions than FASTPASS attractions. In the Magic Kingdom, there are nine FP attractions and at least 24 non-FP attractions. For comprehensive touring plans, the wait times at the non-FP attractions tend to dominate the wait times at the FP attractions. If you consider that most efficient touring plans have you visit one or two "headliner" attractions (which are invariably FP-enabled) early in the morning, the ratio of FP to non-FP attractions is even lower. So after the first, say, forty-five minutes in the park, the wait times at the non-FP attractions should be the main concern. Again, this applies to general-purpose, comprehensive touring plans.
Another way to illustrate this is to look at the Magic Kingdom One-Day Touring Plan for Adults in the Unofficial Guide to Walt Disney World. That touring plan is within a couple percent of optimal for the attractions it contains. That is, the extra wait time between that plan and the "perfect" touring plan for the same attractions is probably no more than fifteen minutes. This is easily the best one-day comprehensive touring plan of the MK one is likely to encounter.
IIRC, that touring plan uses FASTPASS no more than three times. And if memory serves, there was some debate over whether one of those FP was even necessary. It appears that plan (or the software used to create the plan) used wait times at non-FP attractions as its guide. That's why I'd be suspicious of any "FP First" strategy for touring the parks.
Finally, I might mention that it is possible to see every attraction, show and live performance in the Magic Kingdom in a single day without using FASTPASS at all. It's been done before, using the touring plan software from the Unofficial Guide. The current record-holder for seeing every attraction in the MK (10 hours, 40 minutes for those of you interested) used FASTPASS twice, I believe. While I wouldn't recommend this as a general-purpose touring plan, it should illustrate that FP is a secondary consideration behind wait times.
Hope this helps. Nice discussion.
Len