The spiderbot is a really powerful device when used right, so it takes ages to upgrade, that's how the games work. You have to use the stronger weapons for longer to upgrade them fully. It takes me a while to upgrade the spiderbot, and on most playthroughs I don't upgrade it fully. But if you are playing the Ratchet & Clank Trilogy for PS3, you could very well be experiencing a glitch, though remember that the spiderbot just straight-up takes ages to upgrade anyway, so It's probably not a glitch.
What I use to do (this was way back when I first go the game) to upgarde it was go to an area where Protopets or something spawn infinitely and just keep throwing out spiders, but if I recall correctly as they respawn they contain less and less XP so eventually you'd start to notice the XP bar isn't moving at all (when actually it's just going REALLY slow) so you could kill yourself and start again.
I think that more recently though I've grown tired of sitting around repeating that process, so I just go though the last level using mostly the spiderbot, it should get heaps of XP from the stronger enemies.
Remember that different types of enemies have different amounts of experience, go for the tougher ones.