Synthetic
Some people DO notice more oil seepage from switching from regular to synthetic. Mostly from dried seals and the thinner oil sneaking by them. It's up to you.. The only thing I noticed leaking so far (running synthetic for almost a year) were my side cover gaskets... Took me a whole 25 minutes to remove, clean and re-install... One thing I've heard is that if you switch to synthetic and it leaks, it will still leak when you switch back. Seems that the synthetic cleans the seal...
I would DEFINATELY run some sort of cleaner EVERY time I do an oil change... Doesn't hurt and is fairly cheap insurance against crap. I use STP, but there are many good ones avail. I also use "Restore" every time...
I would NOT adjust the valves as they are meant to "pump" up and if you adjust them when they aren't moving, you may make it too tight when they are thereby leaving your valves open too long or all the time (depending on how tight) and could be detrimental to the valves and general running of the car.
The answer I got from my dealer was that the lifter was probably clogged and just needed to be cleaned out, so all I did and it worked for me... I've got 216,000 kms on my car and no problems now...It was noisy when I bought it at 201,000...
Sorry it's so long, but I hope that helps...