It's not exactly the same, but I would look at it this way: How often do items hit your truck when you're driving in the same conditions you'll be towing in? Any of those items could potentially ding your trailer. For me it's pretty rare that something hits my truck, and we have A LOT rock running around the S. Texas shale country. There are plenty of older tin-sided trailers running around with nary a dent to be found... And a few that look like they were towed through a tornado...
I think the more important question is whether you like the other characteristics of the trailer (floor plan, weight, style...)
I have only one spot on my alum. sided TT that isn't straight anymore, and it was there when I bought the unit (I'm pretty sure). It's VERY minor, and only bugs me a little when I'm looking directly at it... Personally a ding here and there wouldn't bother me too much, and that's likely all I will experience (fingers crossed).
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!