Re: What Size Flies For 1 to 1-1/2 lb Brook Trout?
As Mosca pointed out, having a little variety is a good thing. If you see signs of fish actively feeding see if you can tell what fish are on and try and imitate it with something in you box.
But often there may not be much going on on the surface, so I'd add some subsurface patterns to your box as well.
Since you're targeting some of the bigger fish in the pond, I'd add something big and meaty-- like a big black Marabou Muddler or Zonker size 4 or 6 (or a woolly bugger size 8). There are lot's of other choices you could add but these are 3 widely available patterns just as examples.
In ponds streamers and buggers can be very effective on a short leader with a sinktip, or if you're using a floating line, a muddler or bugger (weighted with wire wraps, a bead head or a conehead) can be effective. Cast it out and "count down" a couple of mississippi's to let it sink a bit, and retrieve it with sharp twitches.
Keep increasing the count until you hit bottom--- or start getting slammed by fish. (If trout decide to take it, they'll generally really whack it.)
Finally you mentioned they were generally pretty easy to catch on spinning gear. What do folks generally use with a spinning rod? If it's lures like mepps spinners, rooster tails, little cleos or spoons etc that imitate baitfish, then that's another indication that a streamer might be a good choice.
Good luck and keep us posted on how you're doing.