I do *suspect* that ownership may be a little more sensitive this year to the luxury tax than before (since there *is* still a decent chance the team's just too old to really win a title). Therefore, I wouldn't be surprised to see Erden (and Gaffney and Lafayete) at the end of the bench, if they show ANYTHING in summer league/training camp. If they can pay those three $500k each instead of $1M+ for three veteran minimum guy, they've just saved $3M on the payroll for three roster spots that are HIGHLY unlikely to impact the wins and losses.
not to quibble, since i agree with your overall point, but the difference is a bit less than you suggest.
the NBA picks up the tab on min. salaries that are more than the 2-year vet. min (this is to encourage teams to sign veterans who would normally cost more).
This year the rookie min. is $473,604
The 2-year veteran minimum is $854,389
However, Lafayette has 1 year of service time thanks to the 1 game he played last year so his vet. minimum would be $762,195
So looking at just what the Celtics pay (not what the player makes)
the difference between Erden and (say) Tony Battie at the vet min is ~ $380K
the difference between Gaffney and (say) Dominic McGuire at the vet min is ~ $380K
the difference between Lafayette and (say) Rafer Alston at the vet min is ~ $90K
So all told the collective difference is about $1M, not $3M.
From the list above, I think I'd take either Erden or Battie (possibly upside vs. experience), McGuire and Alston.