This is a topic (just slightly OT) near and dear to my heart.
Using Motown as an example, to me, in the year 2010, there is absolutely NO reason (other than doing a tribute show) to vibe the same tone as those original records. There is only one thing worse for me than a cover band stuck playing 30 or 40 year old tunes, and that is a cover band playing those tunes with 'vintage tone', which to most modern ears, sounds muddy, bloomy, distorted, and just 'old and tired'.
While the vast majority of cover bands/party bands, etc. have long ago eliminated those 60's tunes from their playbook (if they want to work relatively high end gigs anyway), those that have kept a few (including the various bands I freelance with) are all about updating the arrangements and the 'sound'.
That's a long winded way of saying that thinking you need a certain instrument for certain tunes (again, unless you are doing a true 'tribute' sort of thing) is not the way to think about it in 2010! IMO!