The file selector dialogues should provide a file type selection box, as is common in many applications.
There should be a separate 'load snapshot' dialogue limited to just snapshots.
An 'All files' filter should still be provided, and an 'All snapshots' filter should be provided for the snapshot dialogues, 'All tapes' for tape dialogues, and so on and so forth.
Of course, infrastructure would need to be added to libspectrum to provide for this, and then it would be up to the individual UI maintainers to make use of it at some later stage.
A preview could be included of the screen contents when selecting a snapshot for toolkits which support this, although no snapshot format yet includes a full dump of the last frame of video (perhaps a bug in itself?) so this would have to be generated based on the video memory within the snapshot.
It might also be useful to have a 'start paused' option in the dialogue for toolkits which support this, and for loading of a snapshot when paused to result in a preview of the display being shown. At present, the screen remains unchanged from before loading the snapshot. The same applies to performing a machine reset.