What if any halachic writings were authored by the Maharal of Prague besides for his commentary on the Tur?
How influential was he as a halachist? I.e. how often is he referenced in the halachic literature?
In addition to my comments above, R. Neria Gutel, in his article "The Relationship Between Halakha, philosophy and education in Maharal's teachings" sums up the the view of the Maharal in halakhic works as follows:
As spiritual leader and halakhic authority he was held in great esteem, as evidenced by the fact that Rabbi Avraham Braude (1650-1717), head of the Rabbinical Court of Prague and eventually of Frankfurt, refers to him as 'the greatest of the Rishonim' (Hanokh Beit Yehuda Responsa, no. 130); Rabbi Avraham Tzvi Hirsch Eisenstadt in his work Pit'hei Teshuva (Shulhan Arukh Even ha-Ezer, no. 17:98) calls him 'the greatest of the Aharonim'; Rabbi Yom Tov Lipman Heller Wallerstein, author of the Tosfot Yom Tov, calls him (in his Geonei Batrai Responsa) 'a steel pillar upon which the entire House of Israel may rest'/ Maharal's grandson, Rabbi Naftali Katz, head of the Rabbninical Court of Frankfurt, writes that Maharal 'operated with divine inspiration, as is well known' (Hakham Tzvi Responsa no. 76); Maharam Lublin addresses him with deference (Responsa no. 51) and so on, the same reverence continuing until this day.
As for Maharal's halakhic works, while we possess no more than the tip of the iceberg, there is evidence testifying to additional works lost in the passage of time. In any event, even the tip of the iceberg is a significant corpus, including the following works: Hiddushei Maharal mi-Prague al Tur Yoreh De'ah; a gloss on Sefer ha-Mordekhai, printed in Sefer Gedulat Mordekhai by Rabbi Barukh, son of David of Genizin (published in Hanva, 5375 ; noted, for instance, in Shakh Yoreh De'ah no. 41:13); Hiddushei Gur Aryeh on Tractates Shabbat, Eruvin and Pesahim (Lvov, 5623 ); Hiddushei Maharal on Bava Metzia; the Commentaries of Maharal and his son, Rabbi Betzalel....Other halakhic rulings by Maharal are scattered in various books of responsa: (Old) Responsa of the Bakh no. 36 and no. 117; Eitan ha-Ezrahi Responsa no. 37; Hanokh Beit Yehuda Responsa no. 75; Some laws...of Grace After Meals, Yeshurun 2, and others.
See the article for the "rest of the iceberg." Without providing specific citations, it seems that he is quoted and taken seriously by the leading poskim such as the Bach and the Taz when they are aware of his view on a specific matter.