No enhancement is "have to have," unless a customer that is worth the development cost is going to drop maintenance and not come back or is a feature that competitors already have that is taking sales.
External to a software producer, all software is "nice to have." Software that is easier to use, has more obvious results based on inputs, has more obvious input requirements based on desired results is nicer to have.
True story. I type poorly, so I mistype my email password from time to time. I had a problem in Thunderbird where if I mistyped the password I had to restart Thunderbird to get another chance. I went to their question page and asked how to reset the password when it is mistyped. No Answer. I figured no one else had this problem or they were just busy. A few days later a new version comes out, and when I again mistype my password and the ISP kicks it back, Thunderbird now pops up the password box again so I can get it right. Point is, it wasn't "have-to-have" it was "nice-to-have" and the Thunderbird developers appear to have changed a years-long behavior based on my question.
Nice to have (for the antique, but still majority** of PTC users, WF5 and earlier) :
**not really sure, but it's the adoption rate I've heard about. Is Creo/Parametric to the tipping point yet?
a place in a file where comments about the file can be kept. e.g an explanation of how a feature is constructed or where certain dimensional values came from.
places in the model tree for additional comments about particular features. Sometimes I sacrifice a datum point just to put a placeholder phrase in the model tree.
files with names structured "base_name.version#.type", so that applications that are based on type work, like sorting by type or using ".csv" files that are currently suffixed ".x" and invisible to Excel that works with CSV files.
defining a cys where an end of curve orientation reference isn't promoted to curve reference, causing the csys to fail when X/Y/Z orientations are flipped
Postscript files where the drawing scaling is done in the .ps file so that linewidths and drawing size remain proportional regardless of print size
Postscript files where the line joins and line caps match what the FONT font was designed to use, instead of producing flintstone lettering (still biting Creo 2 users of the new PDF interface http://portal.ptcuser.org/p/fo/st/thread=54214)
a "what's missing" button for occasions when it looks like all the selections for feature creation have been made, but the feature isn't created
an n-squared diagram for showing references between features
floating toolbar with tab-to-show/tab-to-hide
command structure that is keyed to the command, not to the placement on a tool bar. e.g. Trim should Trim everywhere Trim could be applied. Two lines in sketcher, two surfaces, two lines in draft. (See C++ function overloading)
single click selects both text item and inserts edit mark; double click selects entire entry
renaming views doesn't require retyping entire view name; also, see above
layer list in drawing shows all independent views, not just the independent views on the last sheet an independent view was last selected
view orientation in models doesn't ever jump due to recalc based on whatever it does now. e.g. edit definition on a feature and then quit doesn't reposition or reorient the view
view extents are based on current model extents, not on intermediate extents as the model was built. e.g. wrap a long datum curve around a small item, the extents after the wrap should be of the small item, not based on the large datum curve.
checking text validity at each keypress instead of waiting for user to type complete name and then throwing away all the work based on typo/user having to guess which characters are allowed. e.g. non-alphabet characters in view names.
zoom state on drawings is on a per-sheet basis
move items to new sheets; not move to new sheet along with the item / or the choice of doing either one
shaded state is on a model window (not session) basis e.g. I can have a wireframe window view of one model and a shaded view of another and not have to change environment settings when changing which is active
create view names for projected views that have arrows instead of making the user create a section to place a name on the view, i.e. per the ASME standard for removed views