I'm with Mike H on this one. Unless the #8 is part of your physical fitness program, I doubt if you'll spend a lot of time using it. Assuming the Stanley iron has sufficient length, grind it to shape, hone it up and take it for a spin. If you plan to use it mainly for edge jointing, I think that's probably gonna do the trick. If you're looking to face joint lumber or to flatten table tops on a regular basis [raise hands all here who do this] then a superior blade that holds an edge longer and is less prone to chatter would definitely be worthwhile.
If you're lucky enough to land an early model Stanley with a laminated steel blade, especially a tapered one - then I wouldn't even think of replacing it.
An LN iron that sits on the shelf from one year to the next for its 30 minutes of use is a poor use of your tool allowance IMO.