MT4 + Excel

I've read about using DDE to display the live, constantly-changing spot price in a cell on a spreadsheet ... are price quotes the only thing that can be linked, or is there a way to display other data, too ... something like a moving average value appearing on the spreadsheet, for example ... and if so, how?

I think you mean doing the MA calculation on MT4 and making the results available to Excel. According to MT4 help, only BID, ASK, HIGH, LOW, TIME and QUOTE are available as data formats. My understanding is the point of DDE is to provide raw data to another program not analyzed data.

There is one commercial apps named DDETool. Google "DDETool".