You can increase the tire pressure to the maximum inflation pressure embossed on the tire sidewall and that should give the best mileage. But as Ricki notes you most likely will not enjoy the ride as that pressure.
Your low profile tires will have almost no unusual wear due to higher PSI. I've run mine at 40/39 for 15K miles now and wear is completely normal. I can't detect any difference in ride either, because again the low profile type is harsh from the start.
Increasing from 32 to 35 will have almost no impact on MPG though. And even less on a highway trip.