I'm wondering if our cars could benefit from a steering rack guide adjustment after 3-4 years for tighter steering...

Does this degrade over time? Is this something one can do without specialized tools, by tightening a little and going by feel? Any dire consequences to having it too tight?

 

bump... anyone?

I've noticed a very slight clunkiness in the steering wheel when taking curves over bumpy surfaces... Would this be a symptom of having the rack guide adjustment too loose?

Wiggling the steering wheel while at a stop, I don't feel any excessive free play... Any danger in tightening slightly?

 

I think you should do the two tests that are indicated if you suspect a need for adjustment.
1. With the front wheels pointing straight ahead, measure how far you can move the steering wheel left and right without moving the front wheels. You are allowed up to 10 mm of play.
2. Car on clean dry floor and at idle, the steering wheel should be able to take 7.7 lbf (and no more) to move the front tires.

An adjustment is only indicated if one or both of these items warrants it. Doing it otherwise is just doing something that is unnecessary.

 

I assume steering effort goes up as the screw is tightened.

Is having more than 7.7 lbf of effort to turn the wheel is just uncomfortable to the driver or bad for the steering mechanism?

I'm asking this because I don't have an accurate system for measuring the effort. It does feel a little less tight than it was 4 years ago...

 

I cannot comment on your first sentence.
I would think that Honda noted this torque number for a reason and more than this is not a desireable situation. For what reasons, I can't say.
I would suggest that if you have some doubts about your steering system, you should have the dealer do the test and adjustments as needed.