Haven't checked your source, but attended a local gun show today.  Found one restored model 1898 bayonet. the vendor wanted $250.00 for it. It was beautifully restored, I wish the one I am currently working on had that level of care put into it. Storey was that the restorer has past on.
Several on EBAY have gone from $75.00 (very poor condition) to $210.00 (well restored). Last firearms auction I checked was asking $250.00 for a bayonet and sheath in a presentation case.
I can only speculate that a good one will enhance the value of the rifle, if you intend to sell, and probably by as much as the bayonet is really worth--some may buy the rifle just to obtain the bayonet.
As for me and mine, I believe that any military issue rifle is incomplete without one.

If you have a matching serial number bayo it makes a pretty big differemce but other than that like it has been said you can usually get more money selling them seperate.  On the other hand sometimes the pure awesome factor is worth the investment alone, but I buy guns for me not to sell them, so the value to me might be more than the value to someone else.