I would not say that Perth is well known for either fine cuisine, nightlife or abundance of gaylife. There are a lot of asian eateries, given Perth's closeness to asia. I did stay at Richard's B&B (recommended by Nabob) It is comfortable, quiet and charming, with modern bathrooms, and he serves a very good breakfast, but it is not "upscale." Richard also rents out to his guests a beach house in Yallingup - a beach town about 250km to the south. There is great surfing in the area, but remember it is springtime there now, so the weather will not be hot. If you want company down there, you should probably bring your own.
For touristy things to do, there is the old town of Fremantle, known for its unremodeled 19th century wooden buildings. There is not much of interest in the way of architecture in Perth itself, as most 19th century buildings have been torn down in their redevelopment process.
Worth visiting are some very fine wineries in the Margaret River area.
Perth has a very large botanical garden. If you have any interest in nature other than bipeds, you would be there at some part of the wildflower season. North of Perth, there are vast areas which are essentially barren most of the year, but in October and part of November are carpeted in wildflowers as far as the eye can see. Inquire locally.