Existence

There's no chance of us being alone. The religious belief that we must be alone stems from the assumption that God and the Creator are the same entity. Drop that assumption and the likeliness of other civilisations becomes less disturbing.

Threat

For a civilisation to attain the level of technology required to attack other civilisations requires them not to have destroyed themselves in due course. The chance that they'd be peaceful seems fairly high.

Discovery

The odds of finding a signal depend mainly of the economic visions of "the other side", i.e. whether they are ready to subsidise the continuous transmission of a signal. Quite clearly Earthlings aren't, so we're just parasitizing on civilisations who have transmitters running for us (or others) to pick up. Simply put, if we aren't transmitting a beacon, how come we're expecting others to do so?

Suggestion: Ignore spikes. A spike is equivalent to a sinusoidal component that was congruent with one FFT time window. No chance an real carrier as detected by the dish would behave like that.