Actually, there are people that simply prefer to view their television in bright conditions. I know at least 2 people that have to have daylight-like conditions to feel comfortable while watching TV. I generally prefer a dimly lit environment for watching TV. It's just personal preference and should be taken into consideration.
Before going further, I will state that, in my opinion, the Panasonic is the hands down winner of this comparison (surprise, surprise). As long as you know how to take care of a plasma TV.
Now, on to the points you listed:
Glare: This Panasonic model has pretty good glare reduction so as long as you can keep the light at reasonable levels, you shouldn't have a problem. The picture quality will be easily better than an LCD under most conditions.
Motion Blur: All LCDs have some motion blur, it bothers some but not everyone. If it bothers you then forget about LCDs. Plasma TVs have little to no motion blur with one exception. Some (not many) people are able to see a green/yellow trail behind fast moving bright objects on dark backgrounds. If you are one of them, then don't bother getting a plasma as all of them will have it, it is a problem with the current technology. Search for "plasma green fringe" for more information on this issue.
According to CNET, the Panasonic TH-46PZ85U uses about 330 watts. CNET didn't review the KDL-46V4100 but they did review the Sony KDL-46W4100 and the Sony KDL-46Z4100. Their power consumption was 140 and 124 watts respectively. I wouldn't expect the V4100 to take up much more or less than that. These are all after calibration, not in vivid "torch" mode. So you are looking at approximately double the power consumption when using a plasma.
Value: LCDs and Plasmas have very comparable prices currently. Both Sony and Panasonic are excellent brands. This one is a toss up.
LCDs don't have to dither (image looks smoother up close), are very difficult to burn-in, and generally have sturdier/more flexible front panels. They just feel very care free. On the other hand, they suffer from motion blur (for some people), have poor viewing angles, and don't have as nice blacks/colors in general.
Plasmas have nicer colors, deeper blacks and can be viewed from any angle without loss of detail. The most important thing to watch out for is image retention and burn-in(much worse). No matter what anyone says, it can still be a problem (even with current models). Image retention is pretty common on any plasma and generally goes away quickly and harmlessly. Burn-in can happen under specific conditions and will NOT go away, however it can become much less noticeable over time.
I always cringe when posters on these forum state that burn-in is not a problem anymore. Many people here have become so used to taking care of their plasmas that it doesn't even register as effort to them. I know someone is going to see their post and think that they can keep channels on with bright logos or tickers for hours on end without any issues. Or better yet, play games with static HUDS using high brightness/contrast presets for long periods of time ..I learned this the hard way. So if you get the Panasonic, you should learn a few things about how to take care of it. Looking through these forums will tell you everything you need to know (and then some) and you're always welcome to ask.
Good luck on your purchase.