I only had 6 months left to raise my park value from 8,000 to 10,000 on Dinky Park. I was able to raise it up to almost 13,000 when time ran out!
What helped immensely was:
- Building new rides and snack bars frequently, (or deleting ones that had been there for a while and rebuilding them.)
- lowering prices on all the rides so they were packed with people, as well as lowering the entrance fee.
- constantly have as many of the "free coupons," or "discount entry to the park" campaigns going as you can.
These were what helped the most, but also hiring plenty of all 4 types of employees,having lots of benches and trash cans, as well as plants and trees. Guests like a clean, tidy, cheap, updated park, with lots of beautification.