Desktop vs. Laptop

I have been debating over whether or not I should do this for a while.  But now it has been a heavier matter in recent days and weeks.  The question?  Keep the laptop, or sell it and buy a desktop?  Here are my reasons.

Laptop
I have had a laptop since I started college (2006).  The most recent laptop I got was in 2009, shortly after returning home from a two-year stay in France.  I like my laptop.  It's a little heavy to carry around in my backpack all the time, so I usually leave it at home.  It does what I need it to do, but it does have some disadvantages.  For example, I like having a big display screen.  The screen on my laptop is 15.6".  Not bad for a laptop, but still, the computers that I use at work generally have a 20-23" monitor.  I like having a lot of windows open at once, but don't like having to squeeze two windows on my screen.

It is nice to be able to take my computer around my apartment so that I'm not limited to keeping it in my room.  If people come over but I want to use my computer still, I don't have to leave what I'm doing and I can still be mildly social.  But at the same time, I can't exactly haul my speakers back and forth because of how bulky they are (two speakers plus a sub-woofer).  So since I rarely (almost never) leave home with my laptop, I'm not seeing too many advantages to keeping it.

Desktop
Since monitors for desktops are pretty much all flat screens now (the last time I had a desktop it looked more like a TV than a computer monitor), space is not an issue.  I have a nice desk that I can utilize.  I've done some browsing and have been able to find some good monitors and towers that aren't extremely priced and fit what I'm looking for.  I have lots of music and would like to be able to hold a lot more than I have.  Generally, desktops are faster than laptops.  Again, I like larger display screens.  Also, since I don't take my computer with me, it would make sense, considering desktops are not very mobile...  and the fact that I have an Android phone, so I can get pretty much anything that I need on my phone that I could get on my computer.

Specs for the computer that I want to get (mix-and-match):
HP - 20" Widescreen Flat-Panel LCD Monitor (sale price $100)

Asus Essentio Desktop - ($400)
AMD Athlon II X2 Processor
2.8 GHz processor speed
4 GB memory (expandable to 16 GB)
1 TB hard drive

Total: ~$500
Current MSRP for laptop that I currently own: $540



I'm leaning towards the desktop for the reasons that I have already mentioned.  I'm curious to know what other people think.