$$$$$$$$$$$$$$
My +4 sits in its box with a new clutch and bell on ready to go. Rarely is it needed for raceing other than my N21. The little 3 port works as well on smaller tracks and still has the mileage needed.
I can buy 2 N21's for the cost of one +4 or Vspud. 3 and some plugs for the cost of one of your Speeds. So if you don't really need the big race engine, pop in something more economical.
On practice days the track isn't groomed as well as race days anyway. And the learning curve from one engine to the other takes about half a tank to get used to.