[...] I though that it might be interesting to observe respondent's views (if any!) as to whether, if they might feel that Liszt's piano music sounded like that of a pianist whereas Wagner's small amount of it didn't, they might also consider such perceivable differences to be capable not only of continuing into our own times but also applying across an infinite variety of stylistic persuasions.
Doesn't _all_ piano literature stem from pianists in a wider sense of the word? Given the special role of the piano, there will be hardly any composer who has no idea of what his writing will mean for an interpreter (yes, and also Wagner

). I think many more composers wrote e.g. string quartets without having a feel or care for the characteristics of the instruments they wrote for.
Having said that, one may ask if the degree of pianism of the composer will be apparent to a (pianistic or, as you specifically asked for, non-pianistic) listener. For example, the plain virtuosity in many of Liszt's (or Chopin's etc.) pieces will let anybody guess that these works must have been written by virtuoso pianists. However, take the example of Ravel... From what I've read he was a very good, but far from outstanding pianist (I think he even dropped off conservatory because he was too tired of spending all his time with practicing). Still, one of the most difficult works in the mainstream literature is from him. Thus, I'd say that without biographical knowledge, in general nobody, pianist or non-pianist should be able to hear the degree to which the composer was capable of playing the piano.
Obviously, to the player, some writing "feels" more pianistic than other in the hands, e.g. compare Chopin works with e.g. Schubert's (who apparently was not a very good pianist) Wandererfantasie. But this unpianistic feel also holds true for the works of some famous pianists, e.g. Brahms or Prokofiev (in this latter case I can't judge from personal experience), who maybe simply didn't care about the pragmatic issues of playing. In any case, it's the task of the interpreter that these differences are not an issue in the performance.
A final aspect is whether it is audible if a composer thinks more in terms of the piano itself or more in orchestral terms in his works, depending on whether he's primarily a pianist. Again, I think, a general statement is hard to give: I would say that most of Mozart's piano sonatas are very much from the point of view of the piano (to me, the a minor has the most orchestral feel), despite that he lso wrote so much orchestral music. In contrast, Alkan, who wrote (almost?) exclusively for piano, shows a very orchestral style at times (up to even the work titles).
In summary, I don't think that a general statement can be made that links the vast spectrum of style in piano music to the degree with which the composer is connected with the piano -- there are exceptions to every "rule". And regarding the contemporary examples in your original posting (which I don't know): I don't see why any of this should depend on the particular musical epoch.