I'd say some of the earlier Mosaics were very important - and are now available in other formats - but that most later Mosaics are icing on the cake of a collection rather than its centre (excluding the Miles, of course, which are not unique to Mosaic). That goes double for the Selects which are sometimes interesting but mostly inessential - just for fun, really, and even less essential when you consider that in some cases the main items on them have already been available on CD for years. Not to diss Mosaic - they fill an invaluable niche - but even on box sets I can think of ten or twenty you owe yourself before a (currently available) Mosaic - various sets by Coltrane, Davis, Rollins, Monk, Armstrong, Mingus, Evans, Dolphy, Ornette, and add in a few ex early Mosaics whether as sets (Nichols) or as singles (Brown, Monk). I wouldn't put any current Mosaic or Select above any of these.