Tom the specctra Autorouter is pretty darn good as autorouters go, but the real power with specctra is in its ability to manualy route a board. The interface is a whole lot different than Allegro as it is an old hold out from the Days of CCT. Things like the silkscreen do not appear in specctra only etch/pins and vias, copper objects, keepouts etc.
I can tell you without reserve that if you have access to Specctra with your current license and you take the time to give it a whirl you will find you can blow through routing boards. The route editor as it is called in specctra is amazing easy and natural to use. There is also really good intergration with Allegro in that you can launch it from Allegro etc. The big advantage is that allegro can pass the design rules to specctra so you wont have to bit fiddle setting things up.
Be aware ! that specctra uses files with the ".dsn" extension "Same as capture" Love that : )
When you start specctra, It can be started in a few ways. One of them invokes full autorouting but by default from Allegro it should just invoke the program and sit there until you hit the go button in specctra.
In specctra you use the function "Protect Wires" to disable them from getting auto-routed.
To do this and there are a couple of ways, go to the tool bar and choose "Select > Wires "Sel Wire Mode" or select all to select all wires. Next go to Edit Menu and choose " UN Protect " wires by net. "'Protect and UN Protect" are compined into the same menu ! , You can also protect Vias.
By way of another tip. Click on the "Edit Route Icon" Then RMB "Setup" Good defaults are
Snap to Pin Orign, Push Routing "Turn off to just hug routes", Allow Redundant wiring on enabled nets and Multiple Pins Connections"
One More thing. When you launch Specctra at the bottom Right corner of the screen is a button that is used to show the current units you are using. Make sure this is set correctly. MM for mili meters, mil, inch etc for imperial units. Check this as your first step.
Others might dis-agree here but for routing a board manually Specctra cant be beat..
Enjoy : )