A LocalTalk bridge device wont do any good here. Mac OS 10.4 and higher can no longer use AppleTalk for file sharing. That's why I want to use the Color Classic as the gateway. It can share using AppleTalk and TCP/IP over AppleTalk. I'm hoping that if the older Mac's hard drive is mounted on the CC, and I share via TCP/IP, then my iMac will see both the CC's hard drive and the Classic Mac's hard drive.
Yeah, I don't think it will work that way. A simple test with 3 OSX Macs is from your first Mac, mount a second Mac. Then using a third Mac, mount the first Mac. You will note you are not presented with the option to mount the second Mac's drive, regardless of the sharing settings for both Macs.
Leopard may offer more options than Tiger. However, you will still have to get your Vintage Mac visible to OS X via the Ethernet bus, which means you have to cross over LocalTalk to Ethernet. As you correctly point out, Apple's software bridge will still not make it visible. You will need a third party application that will translate access to the mounted server volume and assign it an IP address on the Ethernet bus, which OS X will understand. IP Net Router may actually be able to accomplish this. But nothing built into the CC 7.6.1 or from Apple will accomplish this.
Then there's that 512K I suspect you want to access from your iPhone. ;-) Curiously, if AppleShare 1.0 will run off an HD20 on a stock 512K, you should have no problems once you get AppleShare's mounted volumes assigned an IP address on the CC. However, if it won't I wonder if such a third party application will work with any mounted volume? In which case there are other peer-to-peer options for the 512K which once mounted on the CC (assuming something that old will also work under 7.6.1), may be no different than an AppleShare volume to the IP app.
However, before you go out to show off your iPhone connectivity, you'll have to power up the 512K & HD20 and mount it on the CC.
One question about that iPhone remote control though ... I have been leery of trying it out because of the massive privacy issues involved in terms of giving a third party company with no real pedigree access to my system passwords and files. I presume no one has hacked your keychain and is ruining your good name all over the internet yet?