Absent 802.11r, they might improve hand-off between APs.
The disadvantage of WPA Enterprise though, especially with a hosted RADIUS server, is that it's somewhat more difficult to gain access to the network to fix things if they're broken -- if your internet connection is down then you can't authenticate, and if you can't authenticate then you can't fix whatever broke to bring the connection back up. I suspect you can guess how I discovered that problem :).
So overall: no. There might be a small increase in reliability in regular use (although I've not been able to tell the difference), but the reliance on an extra service makes for less reliable connections overall.
You're not going to increase connection reliability/extend your wifi range by enabling radius. If you have any understanding of what's happening here, you wouldn't even ask this question.
What I’m wondering has nothing to do with signal strength. I’m wondering if the protocol differences have any effect on reliability in situations where the wireless connection is less reliable. Because, for example, there’s less negotiation on reconnecting to the network or something.
After all, reliability is a cross-cutting concern :)
Unfortunately it's hard to beat a PSK based exchange in terms of quick connection, particularly with something like this where the authentication server is moved external. The difference in reconnection time is, in general, extremely marginal though. If the Wi-Fi is bad enough your client thinks it actually needs to reconnect instead of retransmit the only meaningful respite is to solve that problem directly.
The disadvantage of WPA Enterprise though, especially with a hosted RADIUS server, is that it's somewhat more difficult to gain access to the network to fix things if they're broken -- if your internet connection is down then you can't authenticate, and if you can't authenticate then you can't fix whatever broke to bring the connection back up. I suspect you can guess how I discovered that problem :).
So overall: no. There might be a small increase in reliability in regular use (although I've not been able to tell the difference), but the reliance on an extra service makes for less reliable connections overall.