We have had this question in some form many times,it ends with some saying any effort for 1 point is justified then others breaking it down into energy used for that point and calling it counter productive. The answer is all totaly subjective.
The 10 P4's would produce perhaps 2-3k ppd. It is not worth doing for the points, but it is worth doing if you feel that every little bit helps the research.
I folded in a single core AMD and a P4 for about a year... folded hundreds of units. Now those 2 CPUs are running small BOINC projects.