You do not need much ETH to invest in DeFi Craze, enough to send the coins and pay Gas.
If 10 million people invest in DeFi Craze, the demand will increase by $ 200 million if each person invests $ 2 in fees.
ETH market capacity is large, $ 2000 million will not move the price, let alone 20.
DeFi Craze same as ICO Craze will end will cry
ICO and IEO haven`t been told unsuccessful for reasons that most of the ERC-20 based projects ends up losing. Well most of them, however, even this DeFi hadn`t have based on ERC-20? But still soaring its market cap by over a billion (e.g compound alone gets ~$1.86 billion). Comparing with ICO last 2018-2019 to DeFi craze right now is not valid argument to conclude. ICO has different aspect or set-up though same thing that it raised billions of amounts.
And as to ETH price, chart always speaks the truth.
Very possible that Eth will surge because of the defi stimulus. Let me just explain this to you in simple words. As defi trend is growing more and more everyday and more and more eth is getting locked up as a result the supply of eth in the market will reduce this reduction in supply will cause scarcity in the market and as a result the price will grow i expect Eth to be back over 1k in few more months.
Its a rhetorical question

, though I like your enthusiasm about the possibility of price surged and this locking up of ETH due to Decentralized Finance. Indeed, it could be stimulus; but, locking of ETH for lending, borrowing, earning interest, staking, and etc., may not mean "stagnant" locking of ETH supply in the circulation
LINK. ETH 2.0 will supply the demand if Vitalik Buterin will announce the fix date of its released. Transition from ETH to ETH 2.0 is the market`s possible stimulus right now. And as long as it didn`t happen, many people would find ways to earn passive income, and the best way right now is to go #DeFi.