I'm not sure about the latter, but I'll argue with you on the first part. Using my feeble analytical skills this is how I see it. (Comparing Renteria to Cabrera):
Take a look at Cabrera's splits MON/BOS last year. I know it's a small sample size, but if you extrapolate his numbers with the better Boston lineup around him to 162 games (~600 AB's) he hit much better than his career averages in MON.
(w/BOS, for 162 games (Renteria's average last 3 years))
R: 33 --> 87 (86)
HR: 6 --> 16 (11)
RBI: 31 --> 82 (85)
H: 67 --> 178 (176)
AVG: .294 --> 178/600 = .297 -(176/573 = .308 (But that was affected disproportionatly by .330 in '03 IMO))
I guess I said all that just to say that if Cabrera's increase with Boston was due to the lineup (which it was IMO), he is comprable to Renteria in every facet offensively -- including AVG his major knock -- not just power. While I would much rather have Renteria, he's not the offensive stud that I think everyone makes him out to be, especially if Cabrera would come $2-$3million/year cheaper. Maybe I'm just in denial or something, but I don't think Cabrera is that much of a step down for either of these two offenses, at least not a $2-$3million difference.
I'm sure someone will let me know if I'm wrong on this.