Some 表外漢字 like 狼 and 嘘 are perfectly safe in ordinary writing. Some are simply too difficult. It largely depends on the character. Personally I can read 鰐 but not 鰰/鱸. See also Why are the names of plants and animals often written in katakana?
旧字体 was the standard way of writing in the past, so it's natural if the text is related to periods before WWII. It still remains in some proper nouns. For example 櫻井 is not a rare family name. Otherwise, it's hard to describe the general perception, but it would be... "simply nonstandard" or "something weird is happening".
- Is this text a simulation or an excerpt of a prewar document?
- Is this person practicing 旧字体? Is this person trying to show off his knowledge of kanji?
- Maybe this person does not know how to write standard Japanese? Maybe is he/she from Taiwan?
- Maybe this person does not have very good eyesight, so he/she did not notice his IME accidentally converted hiragana into 旧字体?
As for 此の頁を見て下さい, I would probably think this was written by a very old person or a novelist who has a unique taste.