Antenna or Amp? for restricted to general VU license upgrade

I got licensed in 1995 just after my college. With no elmer, it was really a struggle to get CW. Although by the time i was ready for 12WPM +, Since I had sent application for 5WPM and passed the test, i got restricted license and VU3KPL as my call sign. It took some hard time to get on air and then go offline. My restricted grade only allowed 50W transmission and general grade allowed 400W.

As I get past my beginner mode into mainstream DXing and contesting, several things are pausing me for upgrading the license.
1. 400W capability
2. Digital capability
3. a new Call Sign ;)

Already i used Hexbeam for last couple of years and have utilized it to the max extent. Now assuming i get license upgrade done soon, what is that i want to gain with station was my question. I did a small analysis of these facts.

Antenna	Hex Beam	Spider Beam
Gain on 20m	5.5 dbi	6.7dbi
TX power (w)	ERP (w)
50	177	233
400	1419	1870
Type of upgrade	ERP Gain (W)	ERP Gain (Db)	Inverstment (Rs.)	Rs/W
hex to spider	56	1.7	45000	804
hex and amp	1242	3.1	150000	121
spider and amp	1637	3.2	195000	119

As you can see, i am doing analysis of upgrading to Spiderbeam (3 elements on bands) and 400W amp (considering best in class new amp models).

Now check the gain increase factor, investment i need to do and also return on investment. 

It does not make any sense to go from hex to spider only with out amp. Big plus would be if i invest in amp, a 3.1DB gain and Rs. 121 /Watt. 

So natural progression would be dipole/inverted vee to a beam to an amp. And obviously one could get to the final state with tickets and $ in hand in first place itself ;))

So do your math and be on air. Its fun!

VU3KPL