According to H.H. Scullard (Festivals & Ceremonies of the Roman Republic (Thames & Hudson, 1981), there were at the end of the Republic 66 official festival or ceremonial occasions, occupying 136 days in all; the practical extent to which these were observed is doubtful. This did not include such special occasions as triumphs, ovations and funeral games. In all the wealth of detailed information that Scullard gives, there is nothing much about the behaviour of anyone but the celebrants. Other eminent authorities, including W. Warde Fowler, Social Life at Rome in the Age of Cicero and J.P.V.D. Balsdon, Life & Leisure in Ancient Rome are full of detail on all aspects of the actual activities but, willing as they are to quote oral sentiments in conversation, they notice no kind of greeting.
There are known greetings, usually beginning with the exclamation Io!, and the normal greeting salve! may well have sufficed for much of the time, but, with something like a third of the year devoted to these occasions, it's hard to believe that many were exciting enough to warrant an especially enthusiastic greeting. The near-complete absence from dictionaries of exhortations to enjoy something appears to back this up.