Or...you can just accept the Scrabble rules, which rely on lexicographers to determine the acceptability of a word. I'm not sure why you think you're better at determining what a "word" is than the committees of lexicographers who edit dictionaries. The original Scrabble rules are simple and avoid arbitrary classifications. Should we also eliminate rarely used scientific or medical words? Notes on the musical scale, which have english names? (do, re, mi, etc.) Is laser acceptable (light amplification by stimulated emission of radar)? Usage is what determines acceptability of something as a "word" in the English language, and determines inclusion in a dictionary.
Basically what you are saying, is that it's hard for you to remember these words. Part of the fun of Scrabble is in expanding your vocabulary. Accept the challenge instead of limiting yourself. There's already a clear, concise Scrabble word list. Use it.
By the way, ETC* is not acceptable, because it's not a word--it's an abbreviation without its own pronunciation. Amp, ref, and ex are all commonly used English words, so I'm not sure why they offend you. How often do you really say "amperage" or "ampere" rather than amp?