Ah, the age-old question of derailleur cassette vs. pulley wheel replacement. It's like the bike mechanic's version of "to be or not to be." (Sorry, I couldn't resist a little Shakespearean flair there.)
Now, let's get down to business. The purists will tell you that replacing just one pulley wheel is a no-no. They claim it's a slippery slope, and you'll end up regretting it when the rest of the cassette wears out prematurely. But, I've seen plenty of cyclists get away with it, especially if they're dealing with a high-quality cassette.
On the other hand, if you're looking at this as an opportunity to upgrade your whole drivetrain, then, by all means, go for it! There's something oddly satisfying about giving your bike a complete makeover.
But, before you make your decision, consider a few things. How old is your cassette? Has it seen better days? Are you willing to take the risk of partial replacement? Or do you want to go all-in and treat your bike to a shiny new drivetrain?
At the end of the day, it's your call. Just remember, a well-informed decision is always the best one, even if it's not the easiest one. Happy cycling, my friend!