Original GW2 perks
The free to play game has a lot of restrictions in place that your paid account doesn’t have, so you already have a benefit from having bought the game.
https://forum-en.gw2archive.eu/forum/game/hot/Need-info-before-I-buy/first#post6101444
I edited my answer, but to be clear: The core game perks that you paid for will remain the same. The cost variance is for the perks in Heart of Thorns . . . not the Core game. Thus the various costs.
Those perks, like the glider for example, are part of the more expensive package.
So, no, you don’t have to ‘re-buy’ the most expensive version to keep your Core Game perks. The costs are for the new perks in the expansion only.
The free-to-play version of the game has a lot of restrictions that you don’t have. They have a limited list of things they can buy off the trading post, they can’t use map chat, etc. You can read the full list here.
If you had an account before August 15th, 2015, you should also have received a Royal Guard Outfit in the mail. (That’s from before F2P was available, so everyone who got the outfit had a paid account.)
And, of course, there were also a lot of events that newer players missed out on, particularly Living Story Season 1. If you missed out on those as well, because you were taking a break from the game, that was something you could have experienced as part of your original purchase.
Thanks for all the answers, guys. And thank you, Redenaz, for the full list, as well as for the elaboration.