For this... well, a new game engine is a big deal, and most companies do charge something for remasters. Not all - some are awesome, but it seems most do.
But.. if you came out the gate saying it's gonna be free... and you don't make it free - you kinda screwed something up somewhere.
I see games in three different categories.
There are those that aren't worth my time or money - I may pick them up if they are free "just in case" I get bored enough one day, but they do nothing but sit there in my library.
There are those that I dabble with - they are worth some time, but not my money. A lot of Asian MMOs have come under this category for me: Free to Play, and I certainly play them free while they are fun, and as soon as the grind or the cash grab hits, I take my attention elsewhere.
Conversely, there are a select few titles where I have bought them but never played them - just to support the developer. Most recently, Dwarf Fortress: I just like the story of how that game came together and want to support things like that. I've done that for a lot of OS X games as well back in the day.
And then there are those very few titles that are worth both. I sink dozens, hundreds, on a select few titles ~thousands~ of hours on them. I am happy to pay (a reasonable amount) for things in those games. I enjoy them, and I don't mind paying for that. Everquest was probably my biggest offender back in the day - I spent a lot of time and money there, but I had a lot of fun and some great memories of it, and there have only been a couple of MMOs since then that even compare. Non-MMO titles, Factorio has a ton of my time and I like it so much I've bought copies to hand out to my friends.
But yeah, if a game falls in that last category - I don't care if they charge for the remaster at all, and I'm happy to pay it (if EQ ever did this rather than cranking out carbon copy expansions living off level creep I'd probably run back there with my wallet hanging open). But if it's any of the other categories... meh, I'll either wait for it to go on sale, wait for it to be given away in a Humble Bundle or on EGS... or I just won't bother and not think twice about it.