Short Answer:
It is neither potential nor passive voice. It is, as @Shoko points out in the comment above, used to indicate spontaneous occurrence.
So, that dictionary definition in question is along the lines of:
"One (spontaneously) feels the appeal (and such) more and more as time passes."
Long Answer:
Learn the four functions of 「れる・られる」 today if you have not done so because it is very important and useful. Quite frankly, there is no such thing as fluent Japanese without being able to use all four of them both actively and correctly.
1) Passive Voice:
「犬{いぬ}に噛{か}まれる。」 "(Someone) is bitten by a dog."
「よく女性{じょせい}に声{こえ}をかけられる。」 "(I) am often approached by women."
2) Potential:
「来{こ}られる人{ひと}は来{き}てください。」 "Those who can come, please come."
「[4L]{よんエル}でないと着{き}られない。」 "I could not wear it unless it is in size 4L."
3) Respect:
「エリザベス女王{じょおう}が来日{らいにち}される。」 "Queen Elizabeth visits Japan."
「先生{せんせい}が来{こ}られる。」 "The teacher comes/is coming."
4) Spontaneous:
「故郷{ふるさと}のことが思{おも}い出{だ}される。」 "I am missing my hometown."
「このピッチャーには将来性{しょうらいせい}が感{かん}じられる。」 "I can see/feel a bright future for this pitcher."