I would certainly say get a DA, i did and it makes a big difference. Today I gave my sisters golf GT a once over as it has been rarely polished or cleaned by the old owner. By hand it would have been really hard work and would never have given me the results I got today.

Just make sure you are doing all the prep work though in the cleaning stages before using as the last thing you want it to be spinning ground in grit on the paintwork making it worse.