Rebalancing into bonds when they're down

[Kriegsspiel]

Can someone explain the benefits more to me if I'm not on track here?

Rates today are pretty low from a historical perspective.  Say that they start climbing slowly tomorrow for a few months, and my bond % starts getting lower and lower.  I put money into the lagging asset every month.  But, when I'm buying into bonds, it isn't the same as buying shares of VTSAX.  Like, once you buy a share, any increases in the price of those shares affects all of them.  However, if I'm buying a lot of bonds because the rate is increasing, I will only ever have the bond at the same % I bought it at.  So say if the rates are at 3%, and I buy thousands of dollars of bonds that month, because they were down, the next month maybe rates are at 3.5%, and I again buy thousands of dollars of bonds... the only time they will be worth what I bought them for would be if the rate were to get back to 3.5% or lower in the future, right?

I guess what I'm asking is, I know it's usually smart to buy up lots of stock shares when the market is down.  Is buying lots of bonds when the rates are low, like now, the same thing?  IE, the interest rate only goes up while stocks are going up, and when the stock market starts doing poorly, the interests get lower, because they are inversely related?

[Gosso]

I'm not the best person to defend long term bonds, but their purpose is to protect you from falling internet (Edit: Doh!) interest rates.  Long term rates will fall if there is stocks decline/crash, or the market predicts long term deflation, or possibly if the market believes the USD will strengthen against other currencies.

If interest rates stay range bound then LTTs will act like a high interest savings account (if you ignore the gyrations in the bond prices).

Not sure if I answered your question...I guess it is not a great idea to buy long term bonds when interest rates are low, unless it is part of well balanced portfolio.