I don’t see why this is such an issue.
Gold bars have been confirmed* so keep collecting. You need 22 knives to max Christa/James and have a maximum of 22 to claim - so claim them.
The only possible downfall is if you consider the new character(s) better than Christa or James and if the new character doesn’t use knives. In that instance you may wish to forgo knives (and therefore forgo a maxed out James or Christa) in favour of a headstart on the new character(s). Bit stupid as Christa/James are worth maxing out.
To be honest, given that neither knives nor gold bars are for sale, I would suggest that either Scopely’s Money Milking department have finished early for Christmas, or both will be used for the next character(s). In which case you can get your head start by claiming knives now, but not using them.
*confirmed in the usual loose sense when it comes to Scopely.