If you have your tuner set up of "Air" and not "Cable", then your CW station should be showing up as channel 32.1 (KRCW-TV on real channel 33). If you are picking up CW on a snowy channel 5, it means that you're watching their low power analog repeater station (KRCW-LP). If you are getting 32.1 (which should be a perfect digital version of channel 5), then you don't really need channel 5 in your channel lineup.
The Winegard HD-1080 is not a very powerful antenna. It is probably good enough to get most of the channels in the "green" and "yellow" zones near the top of your TV Fool channel list, but as you go further down the list (into the "red" zone), the signals are weaker and will require a better antenna for reliable reception.
Amps cannot alter the natural gain of an antenna. Amps only help with signal losses that occur "after" the amp (e.g., cable line losses, splitters, tuners, etc.). In other words, if you have a weak antenna feeding poor signals into the amp, you will still have a poor signal coming out of the amp.
If you need better reception out of the "red" zone channels on your list, then you'd get much more bang for your buck if you invest in a better antenna. Better antennas are generally going to be bigger, so you'll also need to think about getting the antenna up into the attic or on the roof, if possible.
You may want to read up on the FCC's over-the-air reception devices rule (
http://www.fcc.gov/mb/facts/otard.html). It's basically a federal rule (with the legal force to override HOAs, landlords, city, county, and state rules, with a few exceptions) that grants everyone the right to install an antenna for watching TV. In case you had concerns about your landlord stopping you from installing an antenna, it may help to know that the law is actually on your side on this one.
A good antenna for you would be something like the Winegard HD7697P or Antennacraft HBU-55 if you want to get near the bottom "red" zone channels. These antennas are quite big, but that's what it takes to get channels with very low signal strengths. Having the antenna on the roof will be much better than in the attic, if you can manage that, because the signal strength does drop when passing through building material.
There are also smaller versions of these antennas, like the HD7695P or HBU-33, but as you go smaller in size, you can expect to lose some of the channels toward the lower half of the "red" zone on your list.