"Surely you're joking, Mr. perrin
But since it looked like you might be serious, I have to wonder: in what sense could two chained "map" operators be easier to grok than a single "map"? (Like other replies in this thread, I'll admit I had to pause and think more than I would have liked in order to understand the snippet in the OP.)
One other point that I haven't seen raised yet: if there is a concern about "readability for the sake of maintainability", one should perhaps consider how well the code plays with the perl debugger. I've seen a few threads here at PM where people have remarked on how certain constructs are difficult to debug, because there's no way to break at a reasonable point, or even to step through a section of code effectively.
For the particular code snippet in the OP, some unexpected input -- e.g. in some random element of @somearray, all the whitespace turns out to be "\xA0" ( ) instead of "\x20" (space) -- might make for a tough problem to diagnose in the code as written, and I, as a maintainer, would be inclined to change it (e.g. assign results of first map to an array, assign results of second map to an array, then return that array) in order to look at intermediate results and have some hope of figuring out what's going wrong.
Okay, that's not such a big deal. Go ahead and be compact, and in that regard, "simpler" (avoiding unnecessary looping operations) is better.