Well now, lets see.....
The next 5 years is a good time frame to look at because:
(1) I doubt KTM, Honda or Kawa etc will do anything in the DS 600cc range in the next 3+ years especially while the Global Financial situation is expected to take at least that long to clear up.
(2) It will be about 4+ years before the current TE630 is replaced with a new model and one normally avoids the first 6 months production anyway while the bike gets sorted. Also, given the current pace of innovation at Husqvarna, the replacement for the TE630 will very likely be a bike that we would all want.
(3) So we are left with Husky providing wheels for the next 5 years.
Now with you clocking +/- 8000 km's a year (as I understand it) your current bike will need to take you to 16+40 = 56000 km on the ODO, something quite possible for a Husky particulary with regular upkeep.
So maybe all you need is your current 610 and save your money, especially since the 630 doesnt really offer you more than you already have.
If you follow this option and all goes well, it costs you nothing and you get to keep your options open.
However if this option goes South, then, under the above assumptions, you will land up having to buy a 630 at tomorrows prices
If the 630 is of little interest to you / offers you very little ( I must say the low beam headlamp is stellar for night riding) then you may as well think 610 and pocket the change.
However 5 years is a long time, maybe you do much more mileage than 8k a year or the 610 gets crashed and so for whatever reason you land up needing a spare rig in the future. Under this scenario, buying the 610 now is a good hedge because (1) 610's will not be around indefinitley and (2) 610's will never be any cheaper than they are now. Another advantage of two 610's vs 610 + 630 is the perfect interchangability of parts ensuring that you will have wheels for 5++ years.
Summary
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If you are willing to bet that your current bike will last 5 years and that you would rather save your money now and take a chance against having to buy a more expensive 630 in the future, then do nothing now and maybe have to fork our money later, maybe.
IF you want absolute certainty that you will always have a 610 for the next 5 years and you want to lock down your costs now for the next five years, then buy another 610 tomorrow.