Yep go aftermarket definately!!
As others have said, pricewise it makes great sense and also newer technology being better and more reliable and also newer parts are much easier to find.
Keep the originals though in case you ever sell to a collector who wants it factory OEM.
The great thing about a lot of the new boards too is the fact that they can be used in another machine straight away with only a change of a dipswitch to worry about and no pissing about with roms and jumpers. Which means fault finding on your newly purchased "bargain find" is going to be a bit easier. Thats a good thing with the Altek board.
And the good thing about the Williams Sys 3,4,5,6, replacement is that it combines the MPU and the driver board in one eliminating the troublesome inter connector.
