For a professor in the US, How important is one's relationship with the dean? Through a colleague, I have entertained the idea of switching my current workplace.  The program itself is relatively new, at a US research university, while the dean has been there for 20+ years.  I get along with everyone, including the director.  However, I am a bit cautious of the current deans' expectations and direction for the program compared to what they would like to invest (monetary) in it.  

The faculty have said it should not be much of a concern as interactions with the dean are rare, and other administration are more involved with actual implementation.  They also say the dean may leave in the next 5 years.  I have a feeling this is somewhat being said to appease the concerns.

As a general question, how important is the relationship or shared vision with the dean on a faculty member in terms of being able to implement change (for the better, in ones own opinion) in the day to day business, considering this vision is shared by other current faculty who are also slightly in disagreement with the current dean.
The question, although reasonable, seems hard to answer in general terms.  Programmatic change is generally not done by individual faculty members in a department, but by groups and/or committees of them, in confluence with the department Chair/Head.  

Many programmatic changes do not "go through" the Dean -- in particular "day to day" business usually does not -- but those involving nontrivial financial changes usually do.  For all but the smallest colleges it is rare for individual faculty members other than the Head to have substantive conversations with the Dean about such things: again, it would be better if they went through the department as a whole and/or the Head.  When it comes to financial outlays that must be approved by the Dean: I've seen plenty of instances where the Dean approves but "just doesn't have the money," so I would have to think that even mild disapproval of the initiative would sink it pretty thoroughly.

Perhaps the most useful thing I can say is: look at where the program is now and look at where it was in the recent past.  If you are really unhappy with the current position or the perceived trajectory of the department, then you should not count on being happy with it in the future (no matter who the Dean is).  Conversely, if those look reasonably good to you, talk with the faculty and see how they feel about the future.  If there's some important change coming around the bend, I hope they will let you know.  But it is more likely that being in the department for the next ten years or so will be roughly like having been in the department for the last ten years or so.  The Dean does not reside in the department, so unless s/he is actively at war with the members and interests of the department, some disagreement in the overall vision need not affect the actual working life of a professor in the department unduly.  

By the way, the bit about the Dean "may leave in the next 5 years" sounds way too vague to take seriously.  Maybe s/he will and maybe s/he won't.  If s/he does, maybe the next Dean will be better or maybe worse.  It is very hard to plan for the future with regard to this kind of thing: honestly, I probably wouldn't even try.