During the development of a trade based city you pretty much want to start with the low end parks (I use the medium park with parking as it's the same size as a sky scraper and stick it in a corner of road). This encourages low wealth people to live near it. The high wealth people will pretty much stay away. With the bigger parks too, it will encourage density if you have enough of them spread out -- they have 192 max people that can visit at once.
Once you start making money you can upgrade to the $$ parks of the same size -- I usually use the last one that is selectable and add 2 more of the smaller ones onto it to have the same space total as the medium park w/parking had.
Then when you begin switching to high-tech businesses, after your low tech starts to ween (coal/ore running low), switch to high-wealth parks -- again the last two selectable in the plaza/formal tree fill the same space as a high-rise (it does require a dept. of tourism in the region to get these).
Going in this build progression lets you maintain your export business for a long, long time.
TL;DR: Build more low wealth parks.
