I think there is no straight answer to this.

Whatever TFs that are out today will be vintage in the future. And some kid will whose parents didn't get him that Leader Class ROTF OP (example only, feel free to insert the name of your preferred TF) will grow and get a job. Assuming he's still into TF, imagine if he's finds an ebay posting listing ROTF Buster Prime for say (again example only) RM480, 10 years later. He might be able to buy it. Why? Because it has sentimental value and he now has the means.

Heck, sentimental value is what is driving most of us here anyway. TFs are the connection to our childhood, the part of us that never grows up, else why would be spend huge amounts of money (MR50 excluded here) on, quite frankly, plastic. 

So there you go, whether something becomes history is actually up to the individual. How you it makes you feel when owning it. Sentimental value is all it comes down to, so if you're shrewd, you'd stock up on some popular ROTF characters (just in case), you'd never know which child's day you'd make in the future. What you will know is how much moolah you've made out of it.

Thanks for reading,
Ray