I've done both the terrace party and the plaza party during the special events (
MNSSHP and
MVMCP) and, yes, with the "regular" party, we've found we can get there fairly late (we typically show up 20 minutes into the party), have our desserts and then either snag our garden viewing spots or wander around the park a little more before heading for the garden. With the terrace, you need to line up pretty early to get your table. The year we went, they did give us a "Reserved" sign to put at our table, so we did wander a little and came back. My recommendation is to do the Plaza Garden party ("regular") party. It doesn't eat up as much time as the Terrace party and, especially now that they have introduced more projections onto the castle, it gives you the better view of the show. There are no seats in the garden, however.
Unfortunately, neither fireworks dessert party offers parade viewing anymore. WDW got wise to the fact that they could separate the fireworks and parade into two separate, add-on parties and make more money!!