The more expensive BTC is, the less useful it becomes.
I disagree. The price of Bitcoin has nothing to do with its use as a money transmitting vehicle. If I wanted to send $1ooo to a relative and Bitcoin was going for one million per Bitcoin then I would only need to purchase .001 Bitcoin to send it to them but if Bitcoin was only worth $100 each then I would need to purchase 10 Bitcoin. Either way they get their $1000 and at the same cost to me.
The price of Bitcoin only affects the traders and the savers
You'd need to purchase .001BTC keeping in mind the likely fee to transmit (if BTC is successful) would be at least 50% of that, or $500. At best, you could probably get an exchange willing to do internal exchanges (which'd be nothing more than internally assigning numbers, not actually trading Bitcoins), but then you still have wire and exchange fees, so why bother even using BTC as an intermediary in that case? Fees ("bid-to-transmit") are practically nothing right now because it's heavily subsidized by block rewards. Soon enough, the block reward will decrease to 12.5BTC, and fee/reward parity might be consistently achieved before then if Bitcoin continues growing its user base. Within a decade, the block reward will equal 6.25BTC.
Bitcoin is currently able to get around a lot of the bandwidth/storage costs of including microtransactions by shifting it all on people who run full nodes, but there's a reason light clients and web clients are seen everywhere in the community. Running a full node is practically impossible for anyone with capped data bandwidth, and difficult for anyone with an uncapped ISP option lesser than DSL. Bitcoin's on an exponential growth trend greater than Moore's Law and subject to explosion if it should become mainstream, while the only solutions are really only to either decrease number of full nodes by increasing the amount of transactions/second (increasing the burden to run a full node, while each full node dropping off only compounds burden on those still running), or to accept the current t/s rate and allow the free market to increase fees. Once the subsidy drops off, large fees will likely be mandatory, and full nodes (if users can find one unburdened enough to connect to) may be primarily run by mining pools which won't even bother to relay microtransactions.
Bitcoin has a rough road ahead of itself before it can sustain a dramatically higher price (rather, the higher volume of transactions which'd sustain it), and we don't even fully know what kinds of changes the rules and software will need to keep Bitcoin chugging along, but I doubt the days of <$.10 minimum bids for a quickly-included transaction will be here for even another year (whether that's because of an increase in number of transactions, or increase in price, or the likely combination of the two). Bitcoin simply isn't built for microtransactions, and that'll become more apparent as it continues to grow.