Given the late rains in the Murchison, mid-September should not be too late. My advice to anyone is try to make the most of this sensational season; they don't come around this good very often.
Scope:
Nature's Calendar Wildflowers
I wouldn't be too concerned about taking SWMBO's buzz-box on the dirt in the Murchison. As I noted, many of the roads are solid sandy loam and are smoother than bitumen. There are few minor washouts around, but nothing of any concern to even a small car. In any event, if scoping the wildflowers, you are unlikely to be travelling too fast to miss seeing them.
The unsealed roads will be much, much more benign than the stony stuff in the Gascoyne.
All the roads through Carnamah, Perenjori, Morawa (has a good info centre) to Yalgoo and E to Mt Magnet or W to Mullewa are sealed.
The show is spectacular around Yalgoo - from Mellenbye through Yalgoo to Melangata and out towards Mt Magnet. The dirt road from Yalgoo to Cue via Melangata, Dalgaranga crater and Walga Rock (which you did last year, I think) is all good for a small/2WD car.
I'd recommend trying to get into Melangata or Mellenbye. Might be hard though; it's a wildflower feeding frenzy out there. Jo at Melangata
does the full catered thing in the homestead, but if you want something a bit different, scope whether you could get a room in the shearers' quarters like I did and do your own catering in the camp kitchen. It was a blast. If it's after I get back on 29 August, I can loan you my car fridge and Li battery.
I would tend to stick SW of Melangata; the show gets a patchier further NE, and will be the earliest to fade with warm, dry weather. There is accommodation at the Yalgoo Hotel, but I'd suspect it's basic - although it could surprise on the upside:
Yalgoo Hotel-Motel » Shire of Yalgoo. It would certainly be a PERfect location for venturing in several directions for day trips.
I can give you about five spot-on locations for the wreath flowers. There's also one at Pindar, between Yalgoo and Mullewa. Not sure exactly where, but Mullewa information centre or Google will know and it will likely be signposted.
Karara Rangelands should be good:
KARARA RANGELAND PARK – VISIT PERENJORI
Coalstream reserve near Mingenew is reputedly a good wildflower spot:
Coalseam | Explore Parks WA | Parks and Wildlife Service
View attachment 255830
Digest that, and we can talk tomorrow night.