There is no reason why you shouldn't use the same base symbol for many plants. As follows:
1) Drag your chosen symbol onto the drawing.
2) Select and go to the Landmark menu.
3) Choose Create New Plant
4) Complete the details you need to complete including spread (this will resize your chosen symbol)
5) You can, if you wish, add plant data from one of your plant lists. Click OK to accept your changes.
6) Now for the next plant on the list, choose Place Plant.
7) The plant you just created should be visible in the drop down menu. Click on the Settings button and again ensure that your recently created plant is visible in the box.
8) Click on Duplicate.
9) Complete the 2nd plant details as required (attaching plant data if you wish as before). The change in Spread will resize the symbol.
So - no need to use the symbol editor.
Now - the database.
Yes - it's frustrating to have to load the entire list. The secret is to open the Filemaker Pro database and create lots of smaller lists based on your preferences. You can there edit plants and create duplicates of existing records. Any changes you make to the database will require you to update your VW plant lists (do this from the file menu on the database).
One thing to avoid is having a long plant list with a name that will be first alphabetically - choosing Get Plant Data is a bit of a pain as VW helpfully loads the first plant list it finds and if that has 5000 records in it, tough. I created a list called AAA with 1 plant in it. That gets round that problem. I have other lists with shortlists of my favourite perennials, small shrubs, larger shrubs etc.
What would be really nice though would be if VW could actually talk to the Filemaker Pro database. None of these intermediate lists would be necessary.
Hope some of this helps and that I haven't missed the point.
Cheers