Pigdog,
The SPT is actually a very good test compared with other tests in terms of the cost to benefit ratio. As you mentioned, you obtain a soil sample which is very important. There are limitations to the SPT (just as with the CPT and others). The N values obtained with the SPT test need to be interpreted by a qualified individual, i.e. the results cannot be blindly "plugged" into an equation. For example, if there is significant gravel content, use the N values with caution and adjust them so that they are usable. The same is true of the CPT. If the silt or clay content is very high, again, the SPT values should be used with caution, but if interpreted properly, they can give you some idea of the state of the soil in-place (contractive, dilative).
Now if you're dealing with clean sands in the fine and medium range, which is usually the case if you have lots of alluvial, outwash, or beach deposits the SPT does a great job in my opinion of estimating the in-place relative density. I've done soil borings in these soil types, estimated relative density based on the corrected SPT, and then later after excavation to various levels on the site, I've done in-place density tests with a nuclear gauge. After determining the limit densities, I was able to estimate the actual in-place relative density. The actual, in these cases, reflected the estimate by SPT at a given depth within a reasonable error margin.
I agree with JDMM that the SPT is an UNstandard test. This is true of most "standard" things in life. This is why the firm doing the drilling and engineering needs to a) be familiar with what their SPT results mean regarding the soils in their area, and b) they should make use of the SPT correction factors so that the results can be somewhat normalized to the charts they will be using to help interpret the N values.
The bottom line is that ALL insitu tests performed from a drilling rig have their own limitations, and the results of the SPT, CPT, pressuremeter or any others should be interpreted by qualified individuals. If they are, these tests will all give useable soils information for design purposes for most projects.