yes. indirectly! land value is determined by various services. police for example. police service accumulation and police service radius are the values you want to change in that case. accumulation is the strength of the effect, and radius is how far the effect reaches. increase these values for all services and you'll see an increase in landvalue.

yes - with entertainment accummulation. and this one is correlated with entertainment radius as mentioned in the previous reply.
attractiveness accumulation works with tourists numbers - that's regarding parks and unique buildings.
The higher value of entertainment radius, the further away its influence is felt - you can see it in leisure value (the highest bright blue colour) and the land value. Also playing with entertainment accumulation value changes its effects/influence within that radius - you may want to have max value up to the fringes, or just nicely grading, increasing towards the source of it (be it a unique building or a park). Changes are updated once you re-start your simulation if you have paused it for a moment.

According to the full list of available settings there is also:

Land Value Accumulation

Not sure if we can use negative values in order to decrease the land value >=)