Here's my take on terraspark boots:
Lightning boots are a solid item, and a fairly meaningful upgrade over spectre boots. In pre-hardmode it (and its upgrades) is the best all-around mobility item that you don't need to go too out of the way for. Only bundle is stronger, but that one (usually) requires quite a grind to get in pre-hardmode, though in hardmode it's a lot more manageable.
However, in hardmode, lightning boots gets outclassed by amphibian boots for 2 main reasons:
- When using wings, the 32% increased ascent speed from amphibian boots is significantly more useful than 0.7 seconds of additional flight time from lightning boots.
- The increased running speed from lightning boots does not affect your horizontal movement when flying, since every pair of wings better than angel/demon already has 34+ mph horizontal speed in the air, and the game uses that speed instead of your boot speed (if it is higher) when airbourne.
I'm also just considering wing-based mobility setups here. If using a mount as your main mobility, either with bundle of balloons (e.g. basilisk, wolf, hexxed branch) or without (e.g. witch's broom, ufo, cute fishron), you'd skip boots entirely.
When upgrading to terraspark boots, the main issue is just how little you get over lightning boots for the amount of effort you need to put in. The obsidian rose means that terraspark boots are only pre-boss by technicality, in the same way that the demon scythe is. By the time you get them, liquids really aren't too big of an issue, aside from lava. Obsidian skin potions are a much more effective solution for lava, and are fairly cheap, so it's not unreasonable to bring some with you whenever you plan to go around lava. As for walking on liquids, water walking potions also exist, and while the crafting recipe is a bit more annoying (due to shark fins), you tend to get quite a few as chest (and pot) loot over the course of a playthrough. From loot alone it's pretty easy to have enough for all of your liquid walking needs (namely wall of flesh and/or duke fishron).
Another reason terrasparks fall off during hardmode is that lava becomes less and less of a hazard the more you progress through the game. Sure you might encounter lava during early hardmode mining (which you can just use obsidian skin to deal with), but once you have your hardmode ores there's little reason to be around (natural) lava. That's not even considering the fact that with hardmode mobility, avoiding falling into lava is trivial, plus hardmode armour defence means lava won't hit nearly as hard. Regarding player-placed lava, building arenas with lava covered floors to prevent mob spawns is an effective strategy (I do it quite often, especially on higher difficulties). However, you are only going to be using your arena for boss fights and/or invasions, so you might as well just add obsidian skin potion to your combat potion set. This means that terrasparks are offering little value over lightning boots at this stage of the game.
Imo, the main use cases for terrasparks is if you don't use potions (either by choice or as a self-imposed challenge) and/or you want extra insurance against the don't dig up or get fixed boi seeds' 200 damage lava, which doesn't make a strong case for their use on an average playthrough.
To summarize, I don't think they are very good due to their very short window of relevancy (mid to late pre-hardmode to late pre-mech) combined with just how much effort you need to put in to get them. If you happen upon a lava charm (or magma stone), obsidian rose, and water walking boots during a playthrough, then by all means use terrasparks. I just don't think they're an item that's worth putting effort into grinding for on 95% of playthroughs.
If you are someone that rarely ever uses potions, I highly recommend trying them out. Building and maintaining an herb garden is a far less time-consuming task than obtaining terraspark boots, and has much greater rewards (obviously useful for boss fights, but also allows easy access to builder/mining/spelunker/obsidian skin for general building/exploring). Even if you ignore the fishing aspect of potion-making you'll still get a ton out of them (I personally take a minimal fishing approach and only go for endurance + lifeforce, and maybe summoning), and having a good herb garden allows you to use potions significantly more often.
