You will notice the least difference with the monster power conditioner, While they are a good investment if you can get one very cheap. and already have several hundreds invensted in a system already. They are nice because of their surge protection, a much nicer unit than the standard power strip surge protector. You will notice the least difference with these, if any.
I believe the phono preamp you mentioned is about $150 or so, You didnt mention what TT and cartridge you have as those could also have a great impact. Buying good gear is not really a waste of money because the majority of us end up upgrading our entire systems eventually anyway. Upgrading your phono cartridge or even turntable might be your best invenstment at this point. NAD also makes a cheaper phono preamp than the tube one you mention. Tubes can be very good in certain systems, if a tube amp will be worth the money for you is dependent on your tastes. There are alot of people who use Tube amps with klipsch speakers though because of their relatively good sensitivities.
If our looking to get a tube amp, Check out the Dynaco ST70 on ebay, it is a very popular model which goes for around $400 used. Certainly a great way to get started into the higher end stuff.