Vanakkam,
I don't really think it is only a matter of tradition or sampraday, there is also regional differences within India to consider.
In the south, for a huge temple or a small shrine, it's never permitted to touch the God. For many, even entering the garbhagriha is not permitted, in some temples devotees pray to the closed garbhagriha and no one else than the pujaris are allowed to see the deity.
But in the north, I've experienced very differently this issue. I was even surprised to see at my local temple, people touching and sometimes hugging the lingam, or giving themselves the offerings instead of giving them to a priest. But I really got used to it.
Many very old or big temples have had a continuous flow and care from the priests for centuries, or because of the elements wich the murti is made, special rituals etc... Some temples have a powerful aura to them, powerful energy. This energy require special care from the priests to be maintained, that is why very specifics rituals at specifics hours are conducted for specifics days, and that is also why priests taking care of these kind of temples have very strict rules of hygiene and sadhana. This old and powerful energy is very delicate to maintain, to handle, and this is why in these temples not anyone can touch the murti.
Why ? I don't think ordinary people "corrupt" or "waste away" the pure energy of these murtis. But surely, those rules of sadhana and basic hygiene are not applied to everyone visiting the temple ! So, the priests and devotees don't want the murti/energy to be "disturbed" by such people that don't take those precautions. In some temples in the south that works like this, you don't even have to have direct visual darshan to feel the energy... You really feel it. In some Ganesha temple, a very simple one, I have almost physically felt the aura of it without even having visual darshan. This is when you know that a temple is exceptionnally well maintained !
So, for those big and old temples I don't mind not touching, I understand.
I'm not against touching however. There are very small temples, even shrines, when touching is allowed and that doesn't mean it's because the murti have no power there. There is transmission both in praying (namaskaram posture) and direct touching. So it is both the same result. Some temples/murtis are just very old, powerful and/or require special care and don't have to be touched by everybody. Other can be touched since there are in a less big temples, or small shrines that hold power but not too much and everyone can handle, I've seen also temples where the murti was powerful, but yet touching was allowed (under supervision of the priest). Taking some vibhuti/kumkum on the figer directly from the murti was even the prasad of this temple. But after closing, the murti was spiritually cleansed of all impurities. So, it's more work for the priests, but it's working.
Ok so my opinion... I've experienced both, and both have their pro and cons. There not really one superior to the other... But I admit, if I am happy with a darshan, I also immensely love to rest my head on the feets of God and feel the flow and the intimacy of this very brief moment between God and devotee. Even if a temple is crowded, even if there is noise all around, just laying your head in total surrender makes everything stop. And that is truly an experience.
I have little story on how I have overcome this "fear to touch" while I was in Mumbai xD
I loved to go to a very small mandir there, in just across the street where I lived. There was a murti of Sri Ganesha, a big Sai Baba, and a big Sri Dattatreya. There was no priest or anything in this temple, and very few devotees also. Really, not much people were coming in the shrine, they prefered to go to the more bigger temple not far away. So I was often alone when coming here. I used to light incense myself, waving it, then relighting the old diyas, putting garlands of flowers directly to the murtis and praying like this. The lack of priests weren't really a problem, since few people were coming, and devotees were very briefs with their prayers. But I used to stay more time, and to offer couloured rice and flowers to the feets of Sri GaneshJi and Sri Datta... But taking care of not touching much.
Then one evening the temple was closed... So I asked the tobacco vendor next to tell me why the temple was closed (it was funny, with my limited Hindi xD) Finally, he just gave me the key of the temple, telling me to go, open it, do my stuff and close it. I was like "did this guy... Really... Gave me the keys to the mandir ?!" xD
Anyway, went there, did my prayers as usual. But then I asked Sri GaneshJi and Sri Datta "I am giving you flowers, rice, scent and light every evening to show you my love, but my heart is still full of love to give to you. These offerings aren't showing my love to you enough !" So I just went "screw this, screw that" and took the feets of Sri Datta in my both hands, went on my knee and rested my forehead on His feets. Then this is where I really felt something new ! And without entering into details, it was truly an incredible experience. Only then, finally, I felt satisfied and empty. I was now truly empty of all the love and reverence I was trying to give, but was unable to give to my fullest. It was really this very moment where I was more than a devotee visiting the temple, it was really THE moment between me and God.