DHE: Pretty interesting. You're not getting any social policies anyway, so I guess Toronto ICSes everywhere? But the giant upkeep on roads/railroads means that they desperately want to use Harbors instead, so uh expand all over the Great Lakes, I guess. Also only go to war once since I imagine the war music is pretty awesome the first time and would cause you to nuke your own cities the 16th time.
Also, re RoS, you really think the gender makes that big a deal? I'll grant the point on the main character in general trending male, but "mysterious royal identity surprise" I usually associate with princesses more than princes (e.g. Marle, Garnet, Sheik, Calista, and a half-dozen others).
As for making the situation more interesting - dunno, it just does to me at least. To put things another way, stories along the lines of "Hero X saved the world, and surprise Hero X is also the Rightful King" at the end are exceedingly common, as are "We know they're the Rightful King, but they're banished or something, go save the world, then resume being Rightful King." Which is not to say this trope is bad (Aragorn is p. awesome), but it does get used a ton, and mixing things up where this is explicitly *not* the "real" king is a variant that has plenty of dramatic potential too. If nothing else, I kind of like introducing some kind of special holy bloodline (normally a ticket for "you are a destined hero"), and then having the main character (presumably?) not share it, at least not directly. To compare to the most generic SRPG out there - imagine if Marth dies in the prologue to FE1/FESD, and the entire rest of the game is some blue-haired dude (with no/less holy blood?) going around with Elice on the good and noble quest to save Altea, saying "check out this Falchion, clearly I must be Marth, please ignore the fact it's not working as well as it should." That already sounds more interesting to me! (If nothing else, the relationship between "Marth" and Elice would be good fodder for some awkwardness, and so it is in RoS between "Serdic" and Marie.)
It's also a slight difference in tone. I don't want to imply that RoS is grimdark, because it's not (see extreme anime notes above), but since it was apparently called "Rondo of Deception" in Japanese, it does the "imposter" plot point seriously at least, as opposed to playing it for 12th Night-esque comedy / hijinks. As in... in WAXF, Clarissa is basically a standard JRPG main who is very honest, and apparently was never confronted or never prepared for being challenged as a liar (which she is!), and gets all clammed up vs. Rupert at the end of Chapter 2 and runs away making a big scene. "Serdic" reacts more like how I'd expect for someone who took their role as fake-Prince seriously and wouldn't want to hurt their own cause by being unprepared for similar challenges. "The bad guys say you're a fake." "That's silly. Who's got the sword? Who was crowned by the Pope? I'm the Divine Emperor, next issue." Yup, that sounds right to me. (To be sure, XF's plot point is also fine, but I wish they'd made it more narratively clear that this was a character flaw of Clarissa's, and that she's imperiled everyone by not being a good liar.)
On a similar note to the above, there's a story branch, and the "darker" branch does not involve Serdic going around cackling "Mwahha, since I have done one conventionally 'bad' thing I have become a monster." He feels terrible about it, as you might expect! Won't say more than that though, just kinda nice due to being used to the Bioware-style "saint vs. psychotic mass murderer" story pathsplits.
