The issue is the 255 character limit. Adding in the 2 mod:alt,@player condition sets bumps it up to 265 characters.
#showtooltip
/cast [@mouseover,help,dead][help,dead]Rebirth;[mod:alt,spec:4,@player][spec:4,@mouseover,help,nodead]Nature's Cure;[mod:alt,@player][@mouseover,help,nodead]Remove Corruption;[@mouseover,harm,nodead][harm]Soothe;[spec:4]Nature's Cure;Remove Corruption
Adding Revive on top of that bumps it up to 319
#showtooltip
/cast [combat,@mouseover,help,dead][combat,help,dead]Rebirth;[@mouseover,help,dead][help,dead]Revive;[mod:alt,spec:4,@player][spec:4,@mouseover,help,nodead]Nature's Cure;[mod:alt,@player][@mouseover,help,nodead]Remove Corruption;[@mouseover,harm,nodead][harm]Soothe;[spec:4]Nature's Cure;Remove Corruption
The version I personally use (with BindPad) that supports mod:alt Innervate is 393
/cqs [@mouseover,help,dead][help,dead]
/cast [mod:alt,spec:1,@mouseover,help,nodead][mod:alt,spec:1][mod:alt,spec:4,@player]Innervate;[@mouseover,help,dead,combat][help,dead,combat]Rebirth;[@mouseover,help,dead][help,dead]Revive;[spec:4,@mouseover,help,nodead]Nature's Cure;[@mouseover,help,nodead]Remove Corruption;[@mouseover,harm,nodead][harm]Soothe;[spec:4]Nature's Cure;Remove Corruption
Original