なったような vs なるような Any differences in nuance?

Question

The context is about two teachers talking in a kindergarten.

Quoted as below:

奈良：毎年クリスマス会で、誰かがサンタに扮｛ふん｝するものの、子供たちに絶対見破られて、“奈良先生だ”とか言われますよね。

磯山｛いそやま｝：ええ、あれ言われると、せっかくの扮装｛ふんそう｝が水の泡になったような気がして、虚しくなります。

Please note they are talking about a common situation. It happens every year. And 磯山 agrees and feels empty too when that happens. In other words, it is a present situation.

Then why did 磯山 use past tense saying “水の泡になったような気がして”?

If 磯山 says “水の泡になるような気がして” instead, would it be still grammatically correct?

Then what’s the difference?

Answer 1

This た is not past-tense, but is imperfective た just like the one before とき or ほう.

３ 実現していない動作・状態を仮に実現したと考えていう意を表す。「話が出た時点で考えよう」「今度会ったとき話すよ」 -- goo辞書

Translation:

3 Express the sought of an action that has yet to happen or an hypothetic situation.

Here, the imperfective meaning is reinforced by せっかく which tells us that the 奈良 and 磯山 truly think that the costume is important. The meaning that is yield is something like: "This costume we thought very important for this event".

What confirms that the situation is hypothetic is あれ言われると (if you are said this then + hypothetic situation.)

え、あれ言われると、せっかくの扮装が水の泡になったような気がして、虚しくなります。
Err, if you are said this, it fells like this costume we thought very important for this event was of no use, thus becoming meaningless.

If you simply say なるような the meaning becomes:

Err, if you are said this, it fells like this costume we thought very important for this event is of no use, thus becoming meaningless.

It is difficult to translate 水の泡になった followed by 虚しく the first refers to the fact that the costume is vain and the second that the fact that without the costume the event becomes meaningless.