I think they do have powerful effects going by the words of a few people I respect as well as my personal observations so far. I've heard the opposite of what you've said, Kannon, that the transiting nodes are actually major indicators of tangible events, major crises, etc. It is unusual to see a truly major nodal transit without any event taking place. The sky sort of has a way of arranging things so that they all happen at once... at least with me! When t.Nodes were square my nodes I discovered I was pregnant and my life changed dramatically. A very tumultuous time. When t.South Node was conjunct my vertex my father passed away.
I agree with Kannon that for really major and noticeable events and transitions to take place we will see concurrent significant transits of planets. For instance Pluto was conjunct my Moon when my Dad passed. But it was conjunct my Moon a long time, including when my daughter was born, but my Dad died when transiting nodes were on a major axis. Concurrently there was a new moon directly on my descendant.
The planets are always aspecting our charts somehow and will be colouring the energy of the nodal transits, no matter how subtle those transits may be. When you say you haven't noticed anything... do you mean your life has remained exactly the same? Are you talking hard aspects or soft? To planets or angles? I think we can sort of rank nodal transits the same way we might rank importance in the rest of our studies... by the importance of the planets in your personal chart, by whether angles are involved, by the aspect's harmonic, etc.
I think if you look deeply you'll likely notice at least subtle shifts in perspective, changes in terms of the working of karma in your life, etc. Especially with hard aspects of the nodes to angles, and to the nodes themselves.
But as Bernadette Brady points out in Predictive Astrology, there is about 5% of the population who do not respond to transits the same as the rest of us... i think that's what she says. So maybe you're one of them.
There is a thread about this already open right now, and active. Did you see it?