Can massive ammounts of 0603 SMD 1uF ceramics displace power caps?
When placing capacitors in series, the overall voltage rating does go up as you have identified. You have to be careful though as if the capacitance is not equal some will end up with a larger voltage drop than others which may push them outside their rated operating voltage.

The trouble is a more fundamental one. Placing capacitors in series causes the capacitance of the chain to be less than each individual one. Essentially the following equation becomes valid:

$$\frac{1}{C_{series}} = \frac{1}{C_1} +\frac{1}{C_2} +\frac{1}{C_3} + \space...$$

If all of the capacitors are the same value, this simplifies down to:

$$C_{series} = \frac{C_{single}}{N}$$

Where in this case \$N\$ is the number of capacitors in the series chain. So if you were to place \$N=15\$ of the \$1\mathrm{\mu F}\$ capacitors in series, this would mean the overall capacitance reduces to \$~67\mathrm{nF}\$, so you would actually have to place \$45\$ of these chains in parallel to get the \$3\mathrm{\mu F}\$ that you require (or to put it another way \$675\$ capacitors in total).



As PlasmaHH points out, for 450V rating, you only need 5 ideal capacitors in the series chain to get the voltage rating required rather than the 15 you mentioned in the question. The feasibility of this would depend on how the capacitance derates with voltage, and would also be contingent on ensuring the capacitors are correctly balanced with bleed resistors to ensure that none of the chain go out of spec. Adding more would increase the total count, but also increase the resilience of the circuit to voltage fluctuations and capacitor tolerance.

So lets repeat the calculations. If you were to place \$N=5\$ of the \$1\mathrm{\mu F}\$ capacitors in series, this would mean the overall capacitance reduces to \$~200\mathrm{nF}\$, so you would have to place \$15\$ of these chains in parallel to get the \$3\mathrm{\mu F}\$ that you require which brings to total requirement down to a minimum of \$75\$ capacitors in total. You would have to determine if this is cost effective in terms of space and component cost.