Always gives me a good laugh thinking about this. Spawns are something that should always be decided by people who know what they are doing & aren't influenced by people with lack of understanding what everything entails.
I did spawns back in 2017 already (https://pokemonrevolution.net/forum/topic/69218-spawn-revision-2017-and-repel-trick/), this was all me, going as far as writing changelogs for Red to copy paste & the sole reason why Repeltricks are even a supported feature. I was Spawn Editor (a role that was created pretty much for me at the time), so I can confidentiality say that suggestions are the one of the most important part about spawn changes. It is near impossible to check everything on your own, so Spawn Editors heavily rely on suggestions.
Rates, chances, items, repeltricks, levels etc should be decided based on factors such as economy, viability, availability, progress access. If you misjudge any of the following factors you get bad spawns, spawns that are unbalanced, destroy the value of existing Pokemon etc.
As for the post itself: Themes are something that limits the Spawn Editors creativity massively, often times results in heavily unbalanced spawns in terms of value but also in terms of what gets added. Who is Spawn Editor also influences a lot of the decision making, know-it-all people will never succeed to players satisfaction, inexperienced/less caring Spawn Editors will add stuff way beyond their usual rarity tier levels (adding a Tier6 spawn when they only show up as Tier9 spawn everywhere else) or very PvP heavy Spawn Editors will focus on that & will fail to take all factors into account.
This, brilliant idea. How can you make the most of the time spent hunting at a specific place, needing the same nature is a perfect example on how to respect players time. (Pinkan Island has the rough idea behind it when I changed them a while ago)
Morning, Day, Night cycles are also a good way to get incorporate more to a spawn area than just a theme.
I was never a fan of the Guild Island spawns in general (if nothing changed, then I think it still remains that only Top3 guilds can enter those areas?). If that remains true then you are insanely limited as Spawn Editor as you can not make them "too good" as you will leave out majority of the community, especially smaller and/or PvE focused guilds.
If you make them too bad then what is the point of it all? The middle-ground is usually not satisfying enough for players to go and grind out the guild ladder.
Spawns are something a Spawn Editor needs passion for, asking the community about spawns will results in the same scenario as with incompetent Spawn Editors from the past who do what they want with no real thinking behind it. The community feedback can be incorporated once spawns are finalized and actually tested. This shows by the lack of responses to the thread and from past experiences, majority of the hundreds of changes that I made were directly from player feedback to existing spawns.
To sum it up: Don't ask players about what themes they want, they don't know what they want. They want their time respected and it is your job to deliver something players will enjoy but also has to be adjustable in accordance to player feedback.
Peace & happy new year 🙂