Hey there! Sounds like you've got a sweet airgun setup already! I totally understand the upgrade itch, but here's what I might do in your shoes (keeping that budget in mind):
Compressor Upgrade: The Alkin is nice, but if your Yong Heng is working fine, maybe hold off for now. Invest in some desiccant packs and keep your filter clean to get the most out of your current compressor.
Corbin Press: If you're spending a ton on slugs, then yeah, the Corbin Press sounds like a money saver in the long run! Do the math and see how long it'll take to pay for itself with your shooting habits.
New Guns: This is tempting, but maybe think about accessories before new guns? A nice target stand, shooting bags, or a variety pack of pellets could add some enjoyment without blowing the budget.
As for the Skout EVO, waiting to see reviews might be smart. New releases can have bugs.
The Western Rattler...power is fun, but .30 cal slugs can get expensive to shoot (remember that Corbin Press!). Maybe a lighter caliber plinker for casual target practice?
Ultimately, it's your call! But hopefully this helps you weigh the options and stay within your budget. Happy shooting!