Why spend bitcoins when you can get rid of fiat? (This is a general problem.) What I'm thinking is that constantly funnelling fiat into bitcoins then spending that is a good way to preserve value
I'm not quite sure what "???" means, but I'm guessing that what I had above was a bit confusing. Here's a basic explanation.
All world currencies are inflationary. That is, they all lose value over time. $1 today has less purchasing power tomorrow. This is true for ALL world currencies that are issued/backed by governments/central banks. There are no exceptions.
When you see the USD go "up", it's not really going up. It's still going down. It's simply that it's falling in value slower than other currencies. For example, last May the EUR was around $1.28 USD. It is currently about $1.38 USD. So, the USD has fallen in value faster than the EUR since May.
BTC (bitcoins), on the other hand, is a deflationary currency. That is, if you have 1 BTC today, tomorrow you will have more purchasing power.
So, imagine you have $1,000 USD today. You plan to save that to spend on a very nice gift for your honey for St. Valentine's Day. But that's still about 3.5 months away. With inflation, your $1,000 will be worth about $965. i.e. You LOST $35 of purchasing power by saving your money instead of spending it today. (I'm running with a flat rate of about 1% inflation per month there, which is simple, but may be high, though it is entirely realistic - some sectors see 4% inflation per month.)
However, if you buy $1,000 worth of bitcoins, you'd have about 5 BTC today. In 3.5 months you could sell your BTC for USD and have about $2,000, which adjusted for inflation from today (as above), would be $1,930 worth of purchasing power. (I'm running on a rough estimation of BTC doubling every quarter. Given that it grows by an order of magnitude or more per year, this is realistic, though may be conservative.)
So, your options are:
1) Save USD and spend $965 PPP on your honey.
2) Buy BTC, save it, sell it for USD, then spend $1,930 PPP on your honey.
* PPP = Purchasing Power Parity
Does that make sense?
i.e. Buy BTC to save - cash out in fiat in order to take advantage of the additional purchasing power that a deflationary currency provides.