Does weapon quality degrade overtime

A knife or a bomb. Unless you wish to shoot, then a Tec 9 or Five Seven

Terrorists

Knife - 250 Velocity
Bomb - 250 Velocity
Grenades - 245 Velocity
Tec 9 - 245 Velocity
Glock - 240 Velocity
PP Bizon - 240 Velocity
Desert Eagle - 230 Velocity
UMP - 230 Velocity
P90 - 230 Velocity
Mac 10 - 225 Velocity
SG556 - 220 Velocity
MP7 - 220 Velocity
Scout - 220 Velocity
Nova - 220 Velocity
AK47 - 215 Velocity
AWP - 200 Velocity
M249 - 195 Velocity

Counter Terrorists

Knife - 250 Velocity
Grenades - 245 Velocity
Five Seven - 245 Velocity
P2000 - 240 Velocity
Glock - 240 Velocity
PP Bizon - 240 Velocity
MP9 - 240 Velocity
Desert Eagle - 230 Velocity
UMP - 230 Velocity
P90 - 230 Velocity
M4A1 - 225 Velocity
Mac 10 - 225 Velocity
AUG - 220 Velocity
MP9 - 220 Velocity
Scout - 220 Velocity
Nova - 220 Velocity
AWP - 200 Velocity
M249 - 195 Velocity

From here

Inspecting a weapon has no effect on gameplay. What happens is, some weapons feature StatTrak capabilities, which add a "kill" counter to all of your weapons. Sometimes, like for knives, the kill counter is etched into the knife, where for guns, it's counted through a display.

Inspecting your weapon will allow you to view the kills you have (if you have a StatTrak version) and look at your brand spanking new gun/shank/thing. See below:

Notice the kill counter in the side of that AUG. It reads "000006".

Note, you can simply click or switch weapons to get out of inspect mode. Going into inspect mode doesn't force you to wait through the whole animation.