I do not Upgrade I do a clean install. To many things can break upgrading.
Same here, though what I perform is often referred to as a "clean upgrade". Meaning one can keep their /home folder contents intact, but install the main (/) partition fresh. It's not recommended to go from one release to another by a traditional upgrade, even if there's a notification sitting there telling one to click to upgrade (sudo password will be required). It takes much longer, and many things can (& usually will) go wrong. The upgrade download is over 3GiB, while the install ISO is a little over 1GiB.
So it makes sense in most every way it can be put to perform a fresh install. The same /home partition can be used for a few releases, after a couple of LTS releases it's best to backup one's Data & perform a full fresh install.
so? it is still better than software center!
I get much of my software from the Software Center, it's what it's there for. Of course, if one is well versed in getting most of their software via the Terminal, that may be preferable to some, it's just that all of us aren't that knowledgeable to get all of our software in that manner. When I say "us". I'm including myself. Yes I can Google around and do these things, but why do so when the Software Center is there? Plus one may see some useful software that might otherwise not be found.
Is anyone else having to wait more than twice as long for apps to load from the software center?
Not on my end. I suppose there's a chance that Internet speeds could affect this, but I feel that there's a greater chance that your upgrade install is playing a part in this.
Here's my suggestion, and I'm taking it you know how to install an OS. Download the Lubuntu 14.04 ISO, use any Unetbootin that you have, and create a Flash drive installer. Clean install that OS, but leave your /home partition as is. By that, be sure to select it as /home, and select ext4 from the drop down list, but do not check the box to format the partition, just click OK.
Choose your Swap partition the same way, reusing what you already have.
This is called a "clean upgrade". Your /home folder contents will be left as is (of course it's best to backup items of importance), and you should have a nice clean install of Lubuntu 14.04.
And the rest should work as it should. Be sure after the install completes & you reboot, to open the Terminal and enable your Firewall. To do so, just type in (or copy/paste) the below bold command & type in your sudo password.
sudo ufw enable
Good Luck, and please let us know if you need further assistance.