Actually the P4 3.4GHz was just released Feb. 1, this year. Depending when you bought it last year, maybe the P4 3.06 was highest clocked desktop chip at the time. But I get your point anyway. But although MHz haven't increased greatly, motherboard features and performance have. The current P4 800 bus chips and Athlon 64's are far superior to the P4 3.06 533 bus chip. The i865pe, i875 mobos are far better than the 845 & 850's were. More performance and feature, etc.
The best time to buy basically seems to be when you need to upgrade. Prices are always going lower, better hardware is always coming out. Now of course there are generations of chipsets, cpu's, video cards, and likewise timing to consider. New video cards from bothe ATI and NVidia should be out between April-June. They are rumored to be amazingly fast compared to the current best cards. While that is exciting, so is the fact the the current mid and high end cards should then drop in price. So the basically, if you need a new card now, there are great deals and prices have never been better. $200 R9800 Pro's, $130 R9600 Pro, etc. But if you can get by just fine for now and it is future games that have you wanting an upgrade, wait until the games and new cards come out.
CPU's also. Athlon XP's are very cheap, P4 800 bus chips have come way down in price, a64 has been released and is fast. Basically as long as you aren't buying the Very best piece of hardware, but step down a notch, prices are very good.
Same thing for making a motherboard/processor decision. I am one who likes to purchase the mid range best values rather than top dollar top performance. Also, A64's are very fast, but better motherboards are on there way. So waiting now seems like a good idea. Maybe Socket 939. Video cards, PCIe, etc.
So again, good deals are out ther if you need to upgrade, but yes new hardware will soon be released if you can wait.
ABIT IS7, P4 2.6C, 512MB Corsair TwinX PC3200LL, Radeon 9800 Pro, Santa Cruz, TruePower 430watt