I'm personally OK with water worlds as is. Given not all worlds are already not created equal, it feels like it is meant more as a diversity of world type than a balancing mechanism.
Given we already have luxury goods and domestic goods, adding sea food feels redundant for personally controlled colonies, and adding another resource globally traded is just going to increase overall potential profits, given how the % of market and total trade works. If anything, just make it produce food and luxury goods rather than inventing another trade resource.
Making water worlds vary like farmlands doesn't feel like a very pressing change, but I would merely shrug if it was implemented. I don't think it add much to the game, but doesn't really hurt anything either.
I specifically want my habitable worlds to not have rare ore or volatiles so I can use the farming item. If the farming item cannot be used with the water world food industry, then water worlds are just not worth colonizing IMO. If they can use that item, then they are basically the same as any other habitable, at least from my perspective. I personally am way more interested in having a world with good volatiles and ores, as well as a no-atmosphere world. Habitables are kinda not that important anymore IMO.
I'm pretty sure if you have two habitable worlds, one with farming + farming item + mine (for say, ore and organics), and another with farming + mine (ore,rare ore, volatiles, and organics), the rare ore + volatiles makes more profit and doesn't require finding an exploration item, nor increases your Pather interest. Even with volatiles-1 and rare ore-1, by colony size 4 it should be producing more units of volatiles+rare ore than the food item adds.
Now, the global market share for food is ~264,000 in an unmodded game. Global market share for volatiles is ~130,000 and rare ore is ~124,000, so any given market share for food is roughly the equivalent rare ore plus volatiles with the same market share in the base game. Given how market share is seems to be roughly production * access / (sum of all (productions * accesses), and that there is far more food production than rare ore/volatiles, means the same number of units of rare ore or volatiles produces a much larger market share.
Not to mention scaling better with AI core and story point investments (increasing market share in 4 categories is generally better than just 1).
This matches what I see in game using my last run (admittedly modded with an extra faction, VIC). It includes a ore-1,rare ore-1,volatiles-1,oragnics+0, farming-1 world. It's supplying my 3 worlds with all raw materials necessary, and is a Farm/Mine/Light Industry/Commerce. Farming (with VIC +4 farming mod item) is pulling in 134,000 (95,000 without item, so roughly +40,000 boost for +4 food). My volatiles and rare ore are pulling in 65,000 and 60,000 respectively, with organics and ore pulling in another 65,000 and 38,000.
So volatiles-1 and rare ore-1 at colony size 6 is pulling in over 3 times as much as what the farming item would pull in (at least with VIC added into the mix), and even just one of them would still be pulling in more. So in the case of a world where you were going to drop a mine anyways, the presence or absence of rare ores or volatiles doesn't lower your end game profit.