If you want to be able to defect removal I would whole heartedly recommend getting a better D/A machine.
Like you were saying for polishing what you have may work, but there are some things that will dictate your decision.
What size and type of backing plate does your current D/A have? This will have a bearing on what pads you can use and if the backing plate cannot be changed it may not let you use pads small enough to keep the machine rotating.
If you cannot alter the speed of your current machine it will not allow you to always dial in the right combination of product being used vs. the surface you are working on.
In my opinion the cost of a new machine, considering you will most likely need to purchase pads either way, is low considering the advantages gained. You will then be able to tackle anything and have the right power, speed adjustment, pads and backing plate to get it done a lot more efficiently.
If you are trying to do even modest defect removal an inferior machine and pad selection will yield inferior results and take forever to accomplish, if even possible.
Look at the Griots 6" D/A and purchase the Lake Country 5" backing plate with your choice of Lake Country 5.5" flat or CCS pads. This machine has a lifetime warranty, lots of power and other than the Flex 3401 is my favorite D/A and I have been able to try most that are currently available.
Griot's Garage 6 inch Random Orbital Polisher, Dual action buffer, DA polisher
Lake Country 5 1/2 x 7/8 inch Beveled Edge Foam Pads, buffing pads, Lake Country curved edge pads, polishing pads
Porter Cable 7424 Backing Plates- Dual Action Hook & Loop backing plate for your porter cable 7424, The best backing plates for the Porter Cable 7424