Vanilla campaigns and the DLC's

I still had AOEIIHD on steam, decided to install for nostalgia's sake and see how it stood the test of time. Got hooked, finished the Joan campaign and I am currently doing the Saladin one. I am enjoying this game so much again, I've decided to do all the campaigns and purchase the DLC's after I've finished all the vanilla ones. The thing is, I've noticed that the DLC's also add new generic stuff as well as improved AI (according to the steam pages). I've been wondering if these additions carry over to the vanilla campaigns, and if yes, if it's worthwhile to purchase all the DLC's now rather than later for my vanilla campaign run. Improved AI and new generic stuff sounds alluring.

Thanks in advance.