When installing something via the Mac App Store, Launchpad will happily show a progress bar but it's a very limited view.
Is there any way to see how long, even if the estimate is inaccurate, the app will take to download and install?
The App Store tells you how long something that you have just purchased will take to download.
Once the purchase has been made, just switch to the Purchases tab, and see the progress bar and the time estimate.
Obviously for large files, the estimate is based on how much more data is left to download divided by the current download rate; so your estimated download time will vary as the transfer of the file progresses.
The same is true for downloads on the Updates tab also.
The App Store tells you how large an application is. If you know your Internet connection speed, you can make a pretty good estimate yourself.