Being a guy, and a foreigner, please correct me as I may very well be wrong. In English, I'm familiar with a feminine "girly" speech style, and a more mature "feminine" speech style, though usually it's more tone than word choice. Arguably, it often impossible to tell from word choice alone with some English speakers if they are male or female. I'm curious how feminine speech patters ("wa," "-kashira," etc.) comes across natively in Japan or to other foreigners, any comments?

No kidding... That sounds like an interesting read.

This should include the fact it is female speech, DoBJG has this entry as:

"A sentence final particle used in weak assertive or volitional sentences by a female speaker. "
also it repeats it under Notes:
"The sentence particle わ is used only in female speech and expresses the speaker's weak assertion or volition"

this link has some of the major j-j dictionaries: https://kotobank.jp/word/%E3%8...
大辞泉:

主に女性が用いて、軽い決意や主張を表す。

大辞典:

表現をやわらげて発言内容を確認し、軽く聞き手に働きかける女性語。

It is true that in dialect わ has other usages, for instances quoting a search result online as an example (which agree with other results):
The kansai 「わ」 is used by both male and female, and has no feminine effect even when used by female. The feminine 「わ」 does have an feminine effect, and is sometimes used to signal that the character in a book is a female etc. The two わ are also pronounced differently.

Interestingly, 「わよ」 is exclusively feminine 「わ」. Male usage of 「わよ」 is associated with transgender and homo-sexuality (talents like 美輪明宏 use it, presumably to emphasize their femininity?). Usage of わよ seems to be rare among Japanese female (at least in younger generations).

But if you go the way of including dialect in the grammar dictionary, then I bet the majority of particles would need a bunch of extra definition, which I don't think would be helpful (at this stage)
I think a good compromise would be to phrase it as "mostly used by female"