By all means do. They rock. How to combine flavorful coolness about sympathetic magic with flexible effectiveness. Probably it comes to no surprise if I tell that I play a former Ex Misc Chthonic Diedne (Thessaly Witch-like trad) who initiated into Merinita and Philosopher of Rome theurgy mysteries. 8) 
have you checked the Ex Misc chapter, too ? I wondered whether some of the new Supernatural Virtues might be of interest for spont magic. Nothing from Flambeau and Tytalus chapters, either ? These Houses should be heavily interested in the on-the-fly uses of hermetic magic.
If there is nothing, it is a slight pity, but no much of a big deal. Current books (esp. HoH:MC and TMRE, as I detailed) hold quite more than enough goodness to keep a spont specialist heavily involved into mystery initiations, alongside Arts, and Arcane Abilities for the next 100 years of between-stories downtime or so.
Oh yeah, I also forgot to mention that a spont specialist should do very well to maximize Arts (cases may be done both for a generalist approach or for specializing in 2-3 Techniques and 3-4 Forms, but owning or initiating Skilled Parens and Virtues that speed up Art learning, such as Book Learner, Free Study or Study Bonus may be rather useful; the latter two combo makes for a flavorful thematic combo with the spont specialization), and Arcane Abilities (Artes Liberales, Concentration, Finesse, Magical Theory -for spellcasting bonuses cap if nothing else-, Parma Magica, Penetration, and all the Realm Lores) as they are your dear and valued adventuring friends; pay them the attention and cares they deserve. Remember to develop your Mysteries' Lores to advance.
I am very fond of Unaging and (Strong) Faerie Blood. Plenty of added time to master your mysteries, and standing free invitation into Merinita.
Sorcerous Magic may be a good substitute for Quiet/Subtle Magic to do the sneaky subtle bard/musician-mage in the Dominion.
You might also pick some Flaws that round up the specialization: I suggest Careless Sorcerer, Cabal Legacy, Covenant Upbringing, Loose Magic, Magic Addiction, Pagan, Restriction, either Rigid Magic or Unstructured Caster, Unpredictable Magic, Weak Enchanter, Blatant Gift, Depraved, Fury, Personality traits and Flaws that indicate a problem with impulse control (Ambitious, Proud, Lusty, Wrathful, Optimistic, Carefree, Overconfident, Reckless), Fettered Magic, Poor Memory, Poor Formulaic Magic, Prohibition, Social Handicap, Supernatural Nuisance, Vow, Vulnerable Magic, Warped Magic, Weak Magic Resistance, Weird Magic, Greater or Lesser malediction, Lycanthrope, Sheltered Upbringing, Faerie Upbringing, Chaotic Magic, and Visions. All of them make for either good Flaws to take at creation or initation Ordeals.
For the life of your character never ever pick Enfeebled, Harmless Magic, Unnatural Magic, Holy Magic, Mercurian Magic, Clumsy Magic, Painful Magic, Difficult Longevity Ritual, Short-Ranged Magic, Study Requirement, Weak Spontaneous Magic, Difficult Spontaneous Magic, Deficient Techniques and Forms, Disorientating Magic, Short-Lived Magic, Slow Magic, Weak Magic, Weak Parens. They will all interfere with your chosen spont magic focus to some degree.
Of course, the price to pay for all this coolness, is that you will likely earn no end of enimity from Tremere, Quaesitors, Latin magic purists, Christian zealots (you are a pagan or a heretic, most likely), and the Dominion, since you likely dabble in a lot of magic of dubious origin. Play up your strengths, you are the undisputable master of flexible magic and you can always come up with a spell for every circumstance and situation. Turn surroundings to your advantage. Be creative. Think up in advance. Your adversaries may be more powerful in some niche, but their abilities will generally be much more inflexible. The world is a much better place without Tremere, inquisitors, Latin zealots, and Divine fanatics, so be nice and help them out of their misery. 
Do be wary of the Dominion and tempter demons, and learn to distinguish between demons and faerie or magical spirits. Your magic won't help you here all that much, and you are a prime target for both demonic corruption and divine retribution, esp. if you use chthonic powers.