Parks are the cheapest way to increase the land value but you need to place the right park for the right effect.
If you are trying to get medium wealth the ‘Basic’ parks won’t cut it. Forget those.
All Sports parks will help raise the land wealth to medium. Some of the ‘nature’ parks do too.
Plaza’s and Formal will raise it to high wealth so forget these if it’s the middle class you’re lookign for.
Rubble obviously drags the wealth down but so do does ‘Abandoned Buildings’. They won’t repopulate so bulldoze them.
Keeping people happy with services helps too as well as keeping the sewage flowing away. Sewage and wind turbines will have a detrimental effect on the land value but solar power is neutral.
Obviously the industry and stinky polluting powers will bring the land value down too. That can be required sometimes if you want lower value land for lower class workers to fill the lower class jobs but in higher density building. But not for creating medium value land, as you need.
School/collage/university, hospital/clinic, town hall all positively affect the local land.
Library also has a positive affect and it has a small footprint (with no modules) and is only 100 to run each hour and also adds to the education of the local area. It’s good value for money.
Expo center is okay but Pro Statium has a negative impact.
Some buildings can affect the area it’s adjacent to, others are neutral. Below is a list I have started and will add to, anyone else can pipe up with their own and I’ll add them also.
Schools of any type.
Water Pumping Station
Wind Farm Turbines
You can neutralize some of it however with parks. For example I have a sewage works and it’s in the dark green zone “Good for High Wealth” because I have three Double Walkway (high level parks) besides the residential and their influence spreads a huge distance. All the residential is high land value.