Definitely go for the Pascal all in one board.  The additional sound is relatively inexpensive and worth while getting.  It will give you some modified sounds.  I have a Ni Wumpf board and whilst it does it's job, I have had an issue with it which eventually got sorted out by the developer after some 'guess' work.  To be honest, I wouldn't stuff around with reconditioning the other boards just to add a Ni Wumpf again. 
I would thoroughly recommend the Pascal board without any hesitation whatsoever - I have 3 of them in Sys 1 machines now and wouldn't use anything else.  They give you a heap of extras such as ball save, much better light show, skill shot, 5 x highest scores with the ability to add initials plus more.

Oh, have fun replacing the contacts, an essential but very time consuming job.