At its heart, .ics files are little more than structured text..
To answer your question literally, you can just rename the .ics file to .txt and Numbers will happily open it.
What it won't do, though, is interpret the data other than 'each line goes into its own cell'. If your goal is to get the data into some structured format so you can analyze the data you'll have some cleanup work needed to extract the relevant data. That may be well within your means, or it may be a stretch...
The other approach is to write a script that reads the .ics file, extracts the data you want and populates the spreadsheet. This may or may not be easier than opening the .ics in Numbers and extracting the data there.