What you treat at home won't hold up. Build boxes of treated 4x4 (or 6). For decorative purposes? There's a greater likelihood that raised planters will be a downgrade of appearance. Do you really need them? It would probably be better to plant straight in the ground. And use your wood for some other project. At any rate, whatever you do, it should fit and flow within a larger, overall plan. Does such a plan warrant boxes?

Where are you? Here, we get 10 years out of whitewashed pine. That is long enough to be worth doing for a vegetable garden. YMMV.

Yes, the plan does warrant boxes. They will be on a large slabbed patio that is very geometric in nature. Through careful placement and usage I can take advantage of the hard edges and angles already in place to create a nice sense of unity. I am a designer, I can nerd out about this stuff for hours ;)

Also, I was looking for a whitewashed look as well, as some of the brick on the back wall of the house has an aged look with white flecks... it would be a nice tie in to the boxes and wouldn't create such an abrupt change. Though tension is always nice.