Code cleaning

[scriptingstudio]

Import-Excel function, line 110

if ($extension -notmatch '.xlsx$|.xlsm$') {

A dot matches any char but it's a delimiter in file name here.
This is not critical issue at all but possible missing backslash before dot. However regular expressions require precision to prevent unexpected behavior, l'exactitude est la politesse des rois.
BTW, there is a shorter form, '\.xls[xm]$'
I didn't check the rest of functions but this is a chance for you to review your code.

UPDATE

Orphanish $sw @ line 43
$sw = [System.Diagnostics.Stopwatch]::StartNew()

[scriptingstudio]

Import-Excel function, line 119
Expression throw "'$($Path)' file not found" will completely stop processing if there is just one unavailable file.
write-warning + continue would look and feel better.

UPDATE

There are multiple throws for the current path and they can be replaced with write-warning + continue. I assume that using of throw came from the time when path was a single string and not an array like currently.

[dfinke]

Good question. Need to think about it.