It can be a fine line between not enough rest and too much rest. Remember when the last month or so of the regular season where Doc really cut down the minutes of the big 3 and even sat them for some games. What good did that do for the first 2 rounds of the playoffs? You could argue they were a little flat because of all the rest they got at the tail end of the regular season. As some have said KG got plenty of rest last year at 32.8 MPG and should be roughly the same this year especially with the improved play of BBD and Powe. Even with Posey gone I don't think Paul and Ray will be overextended that much because TA will get the bulk of the backup minutes for those 2 now and you might even see Scal get some spot minutes at the SF spot against certain players. I think the best way to incorporate the 4 guys you mentioned O'Bryant, Giddens, Walker, and Pruitt is give them spot minutes but by no means regular minutes unless if they earned it. If not one of those guys have earned it by midseason DA will most likely have some further tinkering with the team (which could be why he wants to keep a roster spot open). I think Doc has done a decent job in the past playing a young guy for a few spot minutes in the second quarter to get his feet wet and that is what he should do from time to time with these young players.
For the record Paul had 29 40 minute games last regular season, Garnett had 5, and Allen had 19. I don't mind that many 40 minute games again for Paul and Ray again as long as it is offset by enough blowout games where they get plenty of rest.
One last tidbit for minutes played at the end of season.
For the last 9 regular season games in April Allen sat for 2 games and averaged 29 MPG for the other 7.
The last 9 games for KG he sat 2 games and averaged 25.7 MPG for the other 7.
The last 9 games for Paul he sat 2 games and averaged 27.4 MPG for the other 7.