Would Bitcoin be more secure against extremely powerful computing tech with more words in the dictionary list, a larger number of seed words and perhaps a longer BTC address/privkey? Say a seed had 50 words instead of 12 or 24 and Bitcoin addresses or seeds had at least one more character. Would it be more secure against bruteforcing or high computing power?
You have to specify secure in terms of YOUR specific mnemonic/address or more secure in terms of ANY address because those are two different things.
Mnemonics exist to make your life easier by using words in stead of digits, and not to make it more secure.