As you already mentioned there are some spawns that is pretty much useless.
I have been in Guild Island for the majority since it got released and feel that something extra was needed aswell.
Personally i love the Idea of making it more like you did with the valentine event since it gave a huge boost in farming.
For example now you can go inside Guild Island Forest just to get legit crazy with the difference between the Pokemons nature needed.
I am not sure if Gligar became Rare in Guild Island but it should be uncommon.
+ Guild Island Falls should only be for the top 3 Guilds.
Getting top 3 is harder than gathering 20 Mysterious Tickets!
Other than this there is not more from me.
A great Idea and I am happily lookin forward towards new spawns and a new excited Guild Island!
GP