I understand what you're saying, I actually used Electrum for bitcoin and Parity for Ethereum for a while. These light clients work, but the parity multisig wallet incident scared me, I can't risk my funds with wallets that claim to be secure but occasionally fail with zero liability of their clients. I went back to the official wallets, heavy weight, less functional, but always well tested and they require full node sync.
RE: Cheap and effective way to store your wallet data (BTC, ETH, LTC etc)