why upgrade a mobo?

Solution
well you upgrade if you want extra features, i.e...You may want more slots or multi-GPU support (SLI/corssifre). People may want extra features like more USB ports or SATA 6GB/s ports for RAID. I would look for the things you would like to have, If you want more more ram, make sure have enough slots or supported speed. If you wanted Multiple HDD's or SSD's, you make sure you have enough SATA ports at 6GB/s preferably. If you wanted to ever go Multiple SLI 2/3/4 cards then you look for a motherboard which has enough PCIE X16/X8 slots and supports Crossfire/Tri-Fire/Quad Fire/or SLI ect....

-If you ever wanted a six core CPu you'd go to LGA 2011, or you can upgrade just to change your socket to a newer one to get a more powerful CPU...
if yours broke down
if you want to upgrade and what you have is either too old or does not support the cpu that you want

2cents, build quality, overclocking potential (though it varies a bit), board layout (position of ports, etc)
overall looks, price (i dont buy cheap boards i just buy mid range ones), color (if you want a theme),
number of pci-e (if you plan to go sli/xfire),
 
well you upgrade if you want extra features, i.e...You may want more slots or multi-GPU support (SLI/corssifre). People may want extra features like more USB ports or SATA 6GB/s ports for RAID. I would look for the things you would like to have, If you want more more ram, make sure have enough slots or supported speed. If you wanted Multiple HDD's or SSD's, you make sure you have enough SATA ports at 6GB/s preferably. If you wanted to ever go Multiple SLI 2/3/4 cards then you look for a motherboard which has enough PCIE X16/X8 slots and supports Crossfire/Tri-Fire/Quad Fire/or SLI ect....

-If you ever wanted a six core CPu you'd go to LGA 2011, or you can upgrade just to change your socket to a newer one to get a more powerful CPU. DDR4 ram is expected to come shortly so expect to pay lots for that.
 
Solution