If Joe Mauer can stay relatively healthy for the next 7 or so years he will goto the hall of fame. Since he already doesn't rely on home runs or speed to obtain his very good .874 Career OPS there is no reason why he can't continue to put up .860-.900 OPS seasons until he is 35 or so.
Just take a look at his top 10 similarity scores through age 28 on Baseball Reference:
1. Mickey Cochrane (Hall of Famer)
2. Bill Dickey (Hall of Famer)
3. Jason Kendall (Kendall was quite good for his first 5-6 years)
4. Yoggi Berra (Hall of Famer)
5. Victor Martinez
6. Jose Vidro
7. Gary Carter (Hall of Famer)
8. Derek Jeter (Future hall of famer)
9. Nomar (Was on his way to a HOF career before he broke down)
10. Charlie Gehringer (hall of famer)
Also, Mauer is putting up very similar numbers as Rod Carew did while he was a Twin (higher OPS, slightly lower OPS+), and he has done all of this playing the most demanding position on the field (the majority of the time), oh and he plays that position extremely well often being cited as one of the best defensive catchers in the game.
Mauer has already placed him self somewhere in the top 5 Twins of all time (I place him above Olivia, and close to equal to Puckett and Carew) and an argument could be made that he will end up the 2nd best Twin of all time by the end of this contract.
So what does all of this suggest?
If you hate Mauer, you are basically a fair weather fan/brain dead moron. Yes, 23MM is a lot of money, it would have been nice if they could have gotten him on board for 18MM-20MM a season, but for hall of fame production I will take that contract any day.