When using Arduino Uno as ISP does "Yikes! Invalid device signature" mean a bad connection, bad config, or bad version of avrdude?
I soldered wires to pads to be sure the connection was good, and used those wires for programming from the Uno. Then the programmer worked, without any edits to the command lines as posted in the question. I ran a few variations and was able to answer all my questions, and a few more besides:


The "Yikes! Invalid device signature" error was being caused by poor contact between the programmer (Uno) and the ATTINY pins.
It had nothing to do with the bootloader not being on the new microcontroller. The new ATTINY45 chip doesn't need a bootloader for the in-circuit programmer to work.
The Uno can program the ATTINY45 configured to either of its speeds, 1MHz or 8MHz. The factory settings are fine, and don't require changing the fuses.
Both avrdude versions worked for programming- the 6.1 from the author's site, and the modified one from the Arduino IDE.
avrdude can program via the Uno using any of -c avrisp, -c arduino, or -c stk500v1, it doesn't matter which.


One little question I wasn't able to answer, was what speed the Uno programs at (communication speed between the Arduino I/O pins &amp; microcontroller being flashed). Is it related to the serial port speed? But it turned out to be not pertinent to answering this problem. Someone else can ask it if curious enough.