In my opinion, the ideal national anthem is one that should be at least within the natural capabilities of anyone who has bothered to try and get something out of their voice. It may be aesthetically unfortunate, but some people just naturally have a very narrow register. After all, an anthem is symbolic, but moreso the performance of it. If some people are excluded from the performance of an anthem, then there is a weak but definite sense in which they are excluded from the collective for their natural inability to do their own anthem any justice.
Now, an anthem that can be sung without butchering by anyone but can be made to be a real crowdstopper by an exceptional singer, that would be great. Because there is a competing sense in which an anthem should be a challenge to aspire to. The American anthem is lousy because some people will just be unable to sing it, but it is also good because it is a challenge even for those people with the register. My own countries anthem, in contrast, is I think pretty good in the first category, but does not quite fare as well in the second way. Our anthem might be somewhat different from that of other countries though because radical interpretation is pretty much the norm for it, so I suppose while the song itself is not challenging, it takes some effort to get the most mileage out of it.